There are several ways to do so -
1. Delete all characters on your account and when you make a new (when all are gone) the new character will get a choice of the nation it wishes to be in (the same as when you first started).
2. If / When T3 hold "Envoys" which will allow players to pile into the generally weakest nation(s). This also gives you a title / some gold / some honour.
3. Buy a merc and go through that way (not sure how it works so you would have to ask players who have done it). But Mercs are unneccesarily expensive
4. Though this method is pretty much extinct (as it was cheaper and easier than merc, T3 didn't approve), if you can find an "Exile Scroll" that allows you to give up citizenship, though i believe you would need a "Feonir Exile Warrent" if you are a Feo player.
If you are level 1 - 75 with no real decent gear, or whatever, i suggest playing option 1 and putting anything you value (gold included) into your bank and deleting you character and starting over in a new nation... ofc if you dont mind leveling you could do it at 80+ with no issues either...
I wouldn't hold your breath for option 2.
Option 3 is your choice, its expensive in terms of RL money for what you get... and a lot of hassle.
Option 4, again don't hold your breath.