You’ll probably have to manually remove files, since the uninstall utility won’t run either. You can try following this guide from Microsoft, but it doesn’t cover Office 2008, so you might have to take it with a grain of salt and some common sense: https://support.microsoft.com/en-us/office/uninstall-office-for-mac-eefa1199-5b58-43af-8a3d-b73dc1a8cae3
For a new version of Office, there are two options. Paying the Microsoft 365 subscription, via the Office apps available from the App Store, and getting every new Office version and feature when released;
Or, buying the one time purchase version (of Office 2021, do not buy 2019), from Microsoft’s website, and going to https://setup.office.com/?ms.officeurl=setup to finish setting it up, downloading it, installing it etc.