How can I tell if my lap band has erosion I really want it out?

Endoscopy. If you and your physician suspect erosion you should have an upper endoscopy. By placing a camera into your stomach your doctor can see if the band has eroded through you will need to have your band removed and possibly consider other surgical options if necessary.
2 questions? Erosions can cause pain, nausea, vomiting, bleeding. If you want it removed, talk to your surgeon. Can be done even without erosion present; careful, may regain weight if you do remove it, and don't take measures to prevent weight gain.
A scope. If you want it out, you should talk with your surgeon, and arrange to have it out. But the reason you want it out is the most interesting question- it may be it is too tight, it may be that it is too loose, and it may be that you just don't want to change the lifestyle with the band.