1994 ln106 aftermarket stereo/rear speakers installation

[Cropers]

Wanting to fit an aftermarket stereo, currently have and older stereo with only 4" speakers in the dash. Was hoping to install speakers in the rear as well as bigger in the front (possibly in the door?). wanting to know the best way to go about installing the rear speakers and to upgrade speakers in the front.
Any advice would be greatly appreciated.

regards
Nick