How do I boost my alt character?

I want to run my other character through some dungeons to speed up the leveling process.

I know you can do it if you have a second account but how do I do it if the characters are on the same account?

You can't if they're on the same account. What you can do is buy heirloom items to get bonus xp.

well u cant :p u can use heirlooms indeed to speed up the leveling , or u can just ask someone kind to boost you (ppl are nice in icecrown) .. or buy a boosting service with gold from players