I currently own CCleaner Premium Bundle that expires Jan 2024 and am being offered an upgrade to Premium. It's confusing. Should I do it?
The current version of CCleaner Premium Bundle I have is 6.15.10623d
So you have Premium and you are being offered the same thing again?
It seems a bit early but if it's at a reduced price, (or actually includes extras to what you already have), then you may want to consider it.
You will not lose the time remaining on your current licence, it will be added to the new one (the 'merge' may take a day or two for it to show in CCleaner itself).
It's a way that existing users can take advantage of special offers without losing what they have already paid for.
(Note that pop-up offers in the notification area often only popup the one time, if you dismiss them they are gone until the next offer comes along which can be months later).