About Unity 5.2.1

When you upgrade your unity Does it take another 5 Gb to download or does it Uninstall the old one and replace it with the new one?

Also after upgrading do all your projects get deleted

It uninstalls and replaces. Your projects are kept and you’ll just need to take a few mins to rebuild them for the new version. If your upgrading from unity 4, i believe unity 4 will stay on your system.