The following may apply to your vehicle.
Usually parts of the panel are held on by plastic retainers that can be seen if you just pry the panel away from the door slightly. If so, a special forked tool makes this easy and doesn't destroy the panel cardboard type material. There has to be some method to secure the arm rest to the door or you would pull the panel off every time you closed the door. Sometimes there are small plastic plugs popped in place over the holes and these need to be carefully removed with a small pick or screwdriver in order to get access to the securing screws.Not knowing if the vehicle has side airbags if so leave the job to someone more experienced with air bag procedures.
If no side airbags, after you remove the retainers and screws the panel needs to be raised up off the door in order to move it out of the way. Be careful because you have wiring from the electric windows, door locks, electric mirrors and possibly electric seat controls to contend with and depending on what additional accessories you have maybe more.