Before you update a CMSimple Installation, you should make a backup of the whole installation on your PC.
From CMSimple 5.11 there is no longer a separate update package. The normal download of CMSimple 5.11 or higher now can be used as an update to.
You simply can copy (upload) the unpacked download of CMSimple 5.11 or higher over the existing installation of CMSimple 4 or 5. All settings, installed templates and plugins, changes to the language files etc. are retained.
After the update you can log in with your password, go to:
Settings => System Info
... and check the success of the update.