@deh260583 you can keep or not both versions that are completely independent.
In order not to wait for someone to answer your questions, a good habit to get into is to use the search field.
For example, if you type “GP3 GP4”, you will find this topic Update to GP4 Question
You can safely uninstall GP3. Don’t forget to deactivate your GP3 license first though otherwise it will stay linked to your system. (start GP3 and somewhere in the help menu you can deactivate the license)