Originally posted by panic_now:

Originally posted by HAHAHuH?:

Upgrade = next tier
Leveling = level up current tier

I'm fairly sure that game offers this 'leveling' ... inside an upgrade tab :)

I'm not saying that You are wrong but in my oppinion -the mystery stays unsolved.

This wasn't about opinion or what I thought it was. I was clarifying what OP meant.