Pick a spot where you want to move the A/C vent. This will depend on your personal needs. Drive a screw through the ceiling in this position to mark the spot. Place plastic sheeting underneath.
Map out the current A/C ductwork by going up into the attic or crawl space. Find the ductwork that leads to the A/C vent that you wish to move and mark it with colored tape. Locate the screw sticking up through the ceiling and mark this with tape for reference.
Turn off the power to the A/C unit at the main circuit breaker.
Disconnect the current ductwork from the old vent. There are two main types of ductwork: rigid and flexible. Flexible ductwork is mostly found in newer homes and is much easier to work with. To disconnect this type of duct, loosen the clamp holding it to the vent and pull it off the collar. To disconnect rigid ductwork, you will need to loosen the clamps along the duct or cut apart the duct tape holding it together.
Measure the inside diameter of the ductwork with measuring tape. Using the screw through the drywall as the center point, transfer this measurement to the drywall. Use a keyhole or jigsaw to cut through the drywall. Sand down any rough edges gently.
Slip a vent collar through the hole in the ceiling. Secure with pieces of tape.
Connect the vent collar for the new vent to the A/C blower where the duct for the old vent was connected. If you do not have flexible duct, now may be a good time to convert. Use a sharp knife to cut the duct apart. Secure the blower end and the collar end with clamps.
Connect the vent grill through the ceiling to the collar, securing it with screws and a screwdriver.