If you want to save paint, remove the rear wheel first.

If you don't want to remove the rear wheel and  are brave, you can tape and grease up frame and chainguard, and parts of the wheel rim, remove rhs footboard, lower the kicker all the way, and remove it forwards, but you need to be brave and do it in one swift movement, twisting as you go. If you hesitate half way, or do not twist it enough, it will become jammed between the frame and wheel rim , and whatever you do, you are going to be touching up paint somewhere, so if you have a nice finish, take option one.

This is largely the reason why original chainguards in one piece are very rare, once you have had them off and on a couple of times in a hurry, you either left it off or cut and joined it with screws just behind the front sprocket section. 

Good luck, and let us know how you go.