Most Android cameras have a setting in the camera app itself.
If you open the camera app, hit the menu button (or three dots near the top/bottom of the screen, depending) you should see an option for "settings". Then it is a matter of finding the "resolution" or "Photo size" or something like that.
If this doesn't answer your question, feel free to ask again with a little more info about what you have been able to find or where you have looked.
Even better, join the forum so you can post the question, get responses and reply with further info/questions in the same thread for continuity. (see my signature below)