You do not need your previous version of Finale on your computer in order to install the latest version. You’re welcome to have multiple versions installed but removing previous versions of Finale may improve your computer's overall performance by freeing up disk space.
We would recommend migrating any custom files from your previous versions before uninstalling any versions that you no longer need though. The Migrating Files from Previous Versions of Finale section of the Finale User Manual can show you where those files are if you need a reminder.
Once you're ready to uninstall the previous version, you can take the necessary steps in our Uninstalling Finale Knowledge Base article.
By the way, Finale v26 will ask if you’d like to uninstall Finale v25 when you first install the program. Versions prior to Finale v25 will still need to be manually uninstalled.