It is always best to leave a praying mantis ootheca (egg sack) where the female deposited it. However, if it is in a location such as this, where it might be damaged inadvertently by humans passing by, it might be a good idea to relocate it.  There is no way to be 100% certain that you will not damage the eggs inside of the ootheca while you are relocating it. I would recommend using a very sharp, thin blade, such as a razor blade, to carefully cut the ootheca off of the surface that she has laid the ootheca on. The eggs are on the interior of the ootheca, so you will not damage the eggs as long as you do not penetrate the styrofoam-like protective coating that makes up the exterior. Next, carefully attach the ootheca to a vertical surface in a another location in your yard or garden. Be sure to maintain the original orientation of the ootheca or the eggs will not hatch properly. You can use a pin carefully inserted through the edge of the ootheca, or double sided tape, to affix the ootheca to its new substrate.