Most SMEs do not set out to build “legacy systems.” They build or buy tools that solve a problem, and those tools quietly become essential. Years later, the company depends on an old server under a desk, a custom application nobody can change, or a spreadsheet that only one person understands.
Modernising these systems can feel overwhelming, especially without a large IT team. The good news is that it does not need to happen all at once. This practical guide sets out five steps that any SME can follow to modernise legacy systems safely and cost-effectively.
What counts as a legacy system?
A legacy system is any technology that is still important to the business but has become difficult to maintain, secure or connect with other tools. Common examples in Japanese SMEs include:
- Custom applications built with older technologies, such as VB6 or Microsoft Access
- Excel workbooks with complex VBA macros
- Old on-premises servers and unsupported operating systems
- Outdated versions of ERP, accounting or production management software
- Paper-based processes combined with manual data re-entry
Age alone is not the problem. The warning signs are dependence on one or two people, security gaps, frequent workarounds, and an inability to share data with other systems.
Step 1: Build a complete inventory
You cannot modernise what you cannot see. Start by listing every system and important tool the business relies on. For each one, record:
- What it does and which processes depend on it
- Who uses it, and how often
- What data it stores or exchanges
- What technology it runs on, and whether that technology is still supported
- Who understands and maintains it
Talk to each department, not only IT. Many critical tools, especially spreadsheets, are built and maintained outside the IT function. Most SMEs find more systems than they expected.
Step 2: Prioritise by risk and business value
Not everything needs to change immediately. Score each system on two dimensions.
Risk: Is it unsupported? Does it depend on one person? Does it hold sensitive data without proper protection? Would a failure stop operations?
Value of modernising: Would modernising it save time, reduce errors, enable integration or support growth?
Systems that are both high-risk and high-value go first. Low-risk, low-value tools can wait, or be retired.
Step 3: Choose the right strategy for each system
Each system needs its own decision. The most common strategies are:
| Strategy | What it means | When to use it |
|---|---|---|
| Retire | Switch it off | The tool is no longer needed or duplicates another |
| Replace | Move to packaged software or SaaS | The function is standard (accounting, CRM, HR) |
| Rehost | Move as-is to new infrastructure or the cloud | The application is sound but the hardware or hosting is at risk |
| Replatform | Move with limited changes to a modern platform | Small changes unlock support and security |
| Refactor or rebuild | Redesign and rewrite the application | The logic is valuable and unique, but the code is not maintainable |
For SMEs, replace and retire are often underused. Rebuilding custom software is only worthwhile when the process is genuinely unique and a source of competitive advantage.
Step 4: Migrate in stages, and test carefully
Big-bang replacements carry big risks. Instead:
- Start with one system that offers a quick win and low risk, to build confidence and learn.
- Document business rules before touching anything. The logic hidden in old systems, such as pricing rules or scheduling exceptions, is easily lost.
- Clean your data before migration. Old errors should not be carried into new systems.
- Run in parallel. Where possible, operate old and new systems side by side for a period and compare results.
- Involve users early. The people who use the system every day are your best testers and your most important supporters.
Step 5: Retire the old system and prevent new legacy
A migration is not finished until the old system is switched off. Leaving it running “just in case” doubles maintenance, confuses users and keeps security risks alive. Archive required data according to legal retention rules, then decommission.
Finally, prevent the next generation of legacy systems:
- Keep the inventory up to date
- Prefer supported, standard platforms
- Document custom tools and share knowledge across more than one person
- Review systems regularly, for example once a year
Where to get help
SMEs rarely have all the necessary skills in-house. A practical model is to keep business knowledge, decision-making and testing within the company, while working with external partners for assessment, development and migration capacity. Experienced partners, including offshore teams, can make modernisation affordable for SMEs. Government schemes such as the Digital/AI Introduction Subsidy may also support eligible software adoption; check current guidelines.
Conclusion
Legacy system modernisation is not a single project but a managed journey. By building an inventory, prioritising by risk and value, choosing the right strategy for each system, migrating in stages and retiring what is no longer needed, SMEs can reduce risk and build a stronger foundation for digital transformation.