Hit Shift-T to bring up the title window. Select a title from there.
Here are some ways to have more titles available:
1. Start some tradeskills or fishing. As your tradeskill/fishing skill goes up, you will unlock titles.
2. Earn AA. After certain numbers of AA, titles are unlocked.
3. Complete certain raids.
4. Comeplete your epic quests.
5. Purchase a title/suffix from the Marketplace.
6. I think there are some titles available in LoN.