Well, not knowing whether you have a Mac or PC, you would use the uninstaller found in the PS CC folder (Mac) or Add/Remove Programs in the Control Panel (Windows).
Then you can reinstall using the Creative Cloud Desktop app. There would be an "Install" button next to Photoshop CC if your uninstall went correctly. Don't forget to apply any updates through Help > Updates, since the reinstall would go back to the base version. 14.0 instead of 14.2.1.
Thank you. I forgot to mention it is an iMac so reply very helpful.
One additional thing:
There are two major versions of Photoshop CC now... Photoshop CC, which is 14.x (that Gene mentioned above), and Photoshop CC 2014, which is 15.x and is current now.