Thanks again! Sorry about my terms, I used wrong words on my previous post too. English word "cassette" is nearly same on my language, but that doesn't mean the same part than in english, so I mixed up.

Chain doesn't stay properly on teeth on the smallest sprocket. I think replacing only chain wouldn't be good idea?

I would like to use as similar parts as possible, that's why I asked about that UG-marking. If I change it to Hyperglide, can I use same/same kind of axle or does it need different axle? No need to replace friction shifter and rear derailleur with Hyperglide?

The old axle had scratches, how I know it should be replaced?