You would have to create a new character.

thats why we have different classes, to keep the game social and no soloers

You do receive practice points as you advance through the game, as these allow you to buy cross-class skills with trainers besides your own. At level 15 you have probably received only one, but you receive another at 16 (I think) and every time you finish one of Prospector Zeke's quests (find the Funky Bunches, etc) he gives you one. So you can make a witch doctor who really likes running up to people and thumping them. (My witch doctor likes lurking at the back zapping people while her crew take the hard knocks associated with melee brawls).

Alternatively, you can start a buccaneer, play him or her for awhile, and see which style of play you prefer. I have a character of each class. My witchdoctor always travels with a privateer, but my other four are solo characters at this point. I enjoy all five classes. Maybe a slight nod to the shwashbuckler for style. But the WD is extremely effective (she is the highest, at 38).

One reason we will likely never be able to "change" our class, is that they each have very different advancement quest lines, not main line, but various task quest lines. Something you cant just "switch" after they have been done.