Thank you both on replies.
Yes, UpgradeMODX extra is making it a lot, a lot easier, thank you for that extra
I saw on this page that it's requiring Modx 2.0.x, so that's why I wanted to check first if it's gonna be safe to run an upgrade with this extra only.
One more thing, since Modx 2.1 and 2.2 have a lot of changes (deprecated functions, structure changes) I assume that I should check extras being used on the site for Modx versions they're supporting. Should I disabled all extras before upgrades and turning them one by one or I can disable them later on (I'm afraid of being "trapped" if some of the extras will cause manager internal server errors)?