How to increase .Net version from 5 to 9 in existing project

Pre-Upgrade Checklist & Preparations

Before you start changing things:

• Back up your solution / ensure version control — commit all changes, tag the stable baseline. This ensures you can roll back if something breaks.

• Check all dependencies / NuGet packages — list all third-party NuGet (or internal) packages your project uses. You’ll need to verify whether each has a version compatible with .NET?9, or an alternative.

• Inventory your project types — e.g. are you using Web (ASP.NET), Console, WinForms, WPF, mobile (MAUI), libraries, etc. This matters because some project types may need extra attention when upgrading.

• If you use global.json or explicit SDK locking, check that it’s ready to reference .NET 9 SDK. Otherwise you might end up building with an older or unintended SDK version.

?? Upgrade Process (Step-by-Step)

Here’s a recommended upgrade procedure (similar to what’s used in official guidance with tools + manual changes).

1. Install .NET 9 SDK (and update dev environment / build agents)

   • On your development machine (and on any CI/CD or build servers), install the .NET?9 SDK.

   • If you use a global.json to control SDK version, update it to point to the 9.x SDK. For example:

     {
       "sdk": {
         "version": "9.0.100",
         "rollForward": "latestFeature"
       }
     }
     ``` :contentReference[oaicite:2]{index=2}  
     
     

2. Use .NET Upgrade Assistant — or manual approach

   • The .NET Upgrade Assistant (either via command-line or Visual Studio extension) can guide much of the upgrade. It analyzes your projects, dependencies and suggests what needs to change. Microsoft for Developers+1

   • From CLI, you may run:

     upgrade-assistant upgrade
     

     and follow interactive prompts (select target framework, projects, etc.). Microsoft Learn+1

   • If you prefer manual: open the .csproj (or equivalent) files and update the (or ) from e.g. net5.0 to net9.0. Microsoft Learn+1

3. Restore & update NuGet packages / dependencies

   • After changing the target framework, restore packages (dotnet restore) and then update all packages to versions that support .NET 9. Some packages may drop support or require alternate versions.

   • For packages that don’t support .NET 9, you may need to replace them or accept workarounds. The Upgrade Assistant helps by flagging incompatible dependencies. Microsoft for Developers+1

4. Rebuild the solution / projects — resolve compile errors

   • Build all projects (in correct dependency order). If you have multiple projects (libraries, web, services) — upgrade lower-level (libraries / shared) first, then higher-level depending projects. Microsoft Learn+1

   • Fix any compile-time errors, e.g. removed or changed APIs, changed behavior, configuration differences, etc.

5. Update platform-specific settings (if any)

   • If you use platform-specific targets (e.g. mobile / Android / MAUI, or platform-specific settings), ensure the is correctly set (for example net9.0-android35 if applicable) and update related settings. SilverPC Blog+1

   • Also, in case of MAUI or similar workloads, ensure workloads are installed (dotnet workload install …) and build pipelines / agents updated accordingly. Medium+1

6. Test thoroughly — unit, integration, end-to-end, manual flows

   • Run all existing unit tests and integration tests. Ensure they pass.

   • Perform smoke tests / manual testing for all critical application flows (UI, API, background jobs, etc.).

   • If you have CI/CD pipelines — update pipeline definitions to use .NET 9 SDK and ensure builds & deployments still succeed.

7. Review breaking changes / API removals / behavioral changes

   • Refer to the official “breaking changes” documentation for .NET, to check whether any APIs or behaviors your code relies on have changed or been removed. Microsoft Learn+1

   • For any such potential issues, make necessary code modifications or find replacements.

8. Update documentation / configs / deployment scripts / pipelines

   • Update README / docs to reflect new .NET version.

   • Update any deployment / build / Docker / container / CI/CD pipeline to use .NET 9.

   • If you use global.json, SDK version pinning, ensure those are updated.

9. Smoke-release / staging — then production release

   • Deploy first to a staging or test environment. Monitor for regressions (functional, performance, security).

   • Only after confidence — release to production.