To edit one of your stations, select My Profile, then select Stations from the list on the left.  You can click on the name of a station to bring up the Station Details page.

To remove variety (Artist Seeds or Track Seeds) click the X listed to the right of the desired artist or track.  

This same process also works for removing your Thumbed-up or Thumbed-down tracks. To Add Seeds, click Add to the right of the seed listing.

You can also edit your stations from the homepage by rolling-over the station you'd like to edit, clicking the arrow next to it, then selecting Station Details.

You cannot delete stations from My Profile. You can only delete a station by selecting it in your station list on the homepage.