Guild Wars 2

(how) can I do it?

Go towars character selection screen → Choose World Selection → Select your server you want to transfer too → Click Transfer in the right bottom of your screen → Tadaa!

It all cost gems!

What Xerion said.

You can also transfer for free by deleting all your characters. If you do that everything in your bank and anything tied to your account generally (like achievements you’ve done, story sections you’ve unlocked etc.) will be saved.

Also I’m not saying don’t do it but consider why you want to transfer. The only reasons you’d need to do it is if you want to play with people from a different region (NA or EU) or to play WvW. Everything else is shared – you can play PvE or PvP with people from other servers in your region just by joining their party and then using the ‘join in map’ option on the party menu.