Multiple versions on same machine

multiple versions normally co-exist without a problem on the same machine. when you open a different version of Quartus II on Windows, the environment variables are updated automatically and everything should work fine. on Linux you need to take care of environment variables yourself, so there's no problem there

usually cores come with 1 year of "maintenance" included, meaning you can update to newer versions for free. if the license is "permanent" you can use the last version covered by your maintenance date forever

take a look at your license file to try and decipher the maintenance date on your license. better yet, generate a license on the new Licence Center which will have the date written as a comment