[anaconda] Updating Anaconda fails: Environment Not Writable Error

I had the same issue and the base environment was in C:\ProgramData\Anaconda3. This is the case, when Anaconda is installed for all users.

As a solution, I re-installed Anaconda just for me and now the base environment is in \AppData\Local\Continuum\anaconda3. This now can be updated via conda update without admin privileges.