Upgrading of Designer is done by installation of a new version of the program.
To upgrade Designer to a new version, install program over already the existing one. The old version will be automatically cleaned up at the beginning of the process. If you use additional plugins to Designer (Subclipse, MercurialEclipse, etc.) you might have to reinstall them from their update sites.
If you have installed Designer as a stand-alone application (not as a plug-in into eclipse), update the Designer by installing the new version. Do not try to update the Designer via Check for updates.
If you are installing Designer over an existing installation, the old version of program should not be running.
The upgraded installation needs activating. See Activating.