Speaker Removal Help

I bought new rear speakers for my 99 Buick Regal. I need to know how to get the old ones out. I need to remove the speaker grill cover in the back window so I can get to the screws underneath, but don't know how....HELP. Thanks

The remove the rear speakers you need to remove or loosen the rear speaker shelf/tray. Impossible to do it from the trunk. To remove the rear shelf the rear seat cushions have to be removed. The lower seat cushion has two pull straps located at the edge by the carpeting. Once lower seat cushion is removed unbolt the upper cushion. The rear package tray is held down by plastic retainers and must be lifted up but without breaking anything.