Tell us in detail what you've already tried so that we can help you. We don't even know what messages you're seeing, et cetera.
If you’re not using a trial version, but you’re seeing the message that the update is not applicable, try one of these tips to force the application to be recognized as activated: Sign out of and then back in to Creative Cloud to refresh the activation state. Also, launching the After Effects render engine (not the full After Effects application) can refresh the activation; the render engine doesn’t have the crashing problem that the full unpatched application does. Finally, if neither of these works, uninstalling and then re-installing After Effects CC (12.0) can help.