Trading in an OLD pet for a NEW one

Hi, I just started playing Guild Wars and I want to get rid of my old pet. What is the command to do this and if no command how do I go about it. thanks in advance.

Find a Tamer NPC

you need to find jarrel the tamer. in pre-searing ascalon, he is next to the ranger trainer that gave you the pet quest. after the searing, you can probably find him just outside of ascalon.

Head outta town and down the road to the villiage Devona is in.
Before you get to her cross the bridge over the stream and up the hill, go down the other side and zone/ cross the next bridge.

Follow the trail through the scorpion looking creatures and watch your mini-map or use ALT, shortly you will come to 3 people.
One is the Ranger trainer, another a collector and the third the used animal salesman (Don't buy the CAMEL!!! it is rabid...).
Talk to him and follow the conversation through to the point where you offer your pet and voila...

P.S. The camel part was a joke... :P

Cool thats great thanks allot!!!!