Where can i change my second proffesion?

Anyone know, i heard its after getting ascended, but im not there yet.

Is this in Tyria? Do the 3 ascension missions in the Crystal Desert, beat your doppleganger, go thru Dragon's Lair to get to Droknar's Forge. Vanyi will give you a quest to go back to the desert to visit the towns like Heroes, where NPCs will have "path" quests, one path for each of the 4 professions you don't have. Complete the quest and that 2nd is unlocked.

[edit]

With the NF update, you could also ascend then go to the PvP battle isles and just pay 500g for each one.

Well, make sure you get ascended then, as there is no other way