Q. Can I change my representing organization while my claim is in process?
A. Yes, a claimant, claimant's guardian or VA fiduciary may terminate his or her relationship with an individual representative or a veterans service organization at any time by first informing VA. You may appoint a new representative by using VA forms 21-22 or 21-22a: www.vba.va.gov/pubs/forms/VBA-21-22A-ARE.pdf 
By appointing a new representative, the previous representative is revoked automatically. If you have not appointed a new representative, but want to move forward to revoke representation by your current power of attorney, then adhere to the following:
Any new representative will want to review your claim carefully to offer you the best guidance; this may take some time. Some veterans service organizations do not take representation when an appeal is active at the Board of Veterans Appeals, so please don't wait to seek assistance. Please review all letters from VA carefully and take any required steps to preserve your rights.
Find an American Legion accredited service officer in your state: www.legion.org/serviceofficers