To remove yourself from a team blog, navigate to the Settings | Basic tab for the appropriate blog. If you're an admin member, you'll see a full listing of team members there. Just find your name and click the X next to it.
If you don't have admin rights on the blog, you will see a simpler page, with a Remove yourself from this blog link. Clicking this link will remove you from the blog.
If you remove yourself, your previous posts will still appear on the blog, but you will not be able to make new posts. The blog will no longer appear on your Dashboard or in your profile.