change restore down to maximize on outlook express?

This is probably really simple but I have no idea how to change the "restore down" (double square) icon on outlook express to "maximize". Don't know what happened. When I create a new email, the page doesn't cover the whole screen....about half an inch on the left hand side shows screen behind it, which leaves the X icon "buried" on the right hand side,so I can't close the screen.
Any idea what I did, or how to fix it?
I've tried to "grab" the left side to drag it to the edge, but it won't move.
JanMary1