You don't have to go out and buy maternity jeans, if you have some spare jeans lying around.

Unpick the sides.

Unpick the band from one side to the other and discard.

You have two choices with the zipper.  Cut below the zip from side to side or cut half way through the zip.  If you do the latter make sure you sew some stitches at the cut section so the slider does not come off.  I usually use pliers and take the top silver or gold clip at the top of the zip off and reattached at the top of the cut zipper.  Also cut with the slider down.

Get some good thick stretch fabric.  Fold in half (with a curve upwards in the center, and attach back on to the jeans.  It may be advisable to sew some elastic at the fold before you sew back on to the jeans.

Happy sewing

Judith aka genie