iPod Touch 5 update

I have an old Touch 5 32gb model MD717LL/A. (how come all the models listed in support start with A?)

It is still on version 6.1.3. iOS 8.4.1 is downloaded but I never got around to installing it because I didn't like the changes at the time. Like I didn't want to lose the yellow pad for notes. But I don't care about that anymore. I want to start using it again just to play music which it still does.

8.4.1 is downloaded but the Install Now button doesn't do anything. It is plugged into power and has 12gb free and is on wifi. Can I update this thing? How high can it go? I think I read 9 is the max. But how do I get there? Guess I have to use iTunes on my Windows PC?

It's been acting up. It loses the date when battery is dead.