How Can Infection In The Below Knee Amputation Area Be Treated?

hi my dad has undergone an amputation of the left leg below the knee. its been almost 4 weeks for the surgery n 2 weeks that his stitches have been opened. the doc had asked to visit him after 2 weeks.just met him today morning n he asked me that why had i not changed the dressing, but he had not told me to do so, i was only asked to change the crape bandage, now the wound has infection...............is this a serious problem n whats the solution