ok, firstly, check out "help laws" and
"help tribunal".

It'll give you a better idea of why you became wanted. Chalk it up to a learning experience, and don't let it get you down.

On to how to get rid of the flag. News isn't good, I'm afraid.

Option 1. You find a tribunal to pardon you, and while there are a few who might not make you wanted for assisting a groupmate who was attacked, there are not going to be many (probably none) who will remove a flag set by a nother tribunal.

Option 2. You die. Doesn't have to be a tribunal, so if you are able to steer clear of guard like mobs and town, you can carry on relatively normally, and once you die in a pk with someone, you'll be back to normal. You might have an exp penalty again to reach the next level, but really one extra level worth's of exp is not much out of 51 levels. It is at most about 2% of the total exp a hero gets, before allowing for the fact that higher levels take more exp.