You do NOT have to remove the popcorn to install beadboard.
Use an electric stud finder to find the ceiling joists. Mark the ceiling where each joist is located with a pencil. Extend the marks to the walls below so you can still see the joist marks when you cover the ceiling with the panel.
Prime the beadboard sheets with latex primer. Use a high-nap paint roller to get good coverage of the beadboard. Allow the beadboard to dry completely per primer manufacturer directions.
Paint the beadboard with latex paint and a paint roller. Painting the beadboard before installation will save you a lot of time. Painting the beadboard after installation can be time-consuming, messy and tiring. Let the paint dry completely. Roll on a second coat of latex paint once the first has dried. Allow the paint to dry entirely before installation.
Cut the beadboard to size with a table saw. Take the measurements that you have from the ceiling, and transfer them to the beadboard with a pencil. Place the beadboard on the table saw, and cut it to size.
Apply panel adhesive to the back of the cut beadboard sheets. Use a snake-like pattern to apply the adhesive.
Recruit a couple of partners to help you lift the beadboard sheets into place. In most cases, you can simply place the beadboard sheets over the popcorn on the ceiling. Have your two partners hold the beadboard in place while you use a pneumatic nail gun to nail the sheet to the ceiling joists. Use the marks on the walls to guide you as you nail the beadboard into place. Do this until all of the beadboard is in place.
Fill the nail holes with drywall compound. Dip your finger into the compound, and smooth the compound into the holes. Let the compound dry, and then touch up the beadboard with the latex paint.
Nancy: maybe this will help
you don't need headboard to cover popcorn ceiling . It may optically shrink the height of your room. Use thinest sheetrock instead