With Mondain's Legacy came the Elves and now you can choose to either be an Elf or be a Human, each one of them their own advantages:
Elves:
+20 Maximum Mana
Night sight
Small increased chance to resist

Humans
+10 Maximum Hitpoints
Increased weight capacity

You can change between races by performing 2 different Heritage Quests (one for elf to human, and another for human to elf).

Check http://www.uoguide.com/Elven_Heritage_Quest for the Elven Heritage quest.

Check http://www.uoguide.com/Human_Heritage_Quest for the Human Heritage quest.