Incase of upgrade, do i need to install upgraded opus file or just upload the new license?
You need to do both.
Installing version 12 over the top of version 11 will keep your existing configuration (as long as you don't uninstall first, as that wipes the config).
You'll get the default Opus 12 toolbars, but your old ones will also be backed up so you can switch back to them if you want to: Your old toolbars are still there after you upgrade
Thanks that's clear!