Place the ladder under the ceiling duct. Climb to the top of the ladder. Measure the outside dimensions of the ceiling vent to determine what size cover to install. Purchase the appropriate cover size.
Climb to the top of the ladder. Position the cover over the ceiling vent. If the vent is steel or aluminum, release the cover when it feels secured.
Position the screws into the pre-drilled holes, if the cover does not adhere to the vent with magnets. Tighten the screws. Ensure that the screws are tightened as far as they will turn so the cover is secure. Ceiling covers can cause injury if they fall.