I do know how to do it, but I'm always too scared that I'll spoil the work that I've spent hours on, so I get it framed professionally.
Here's how you do it, though, if you really want to try yourself.
Cut a piece of acid-free board to the size of the inside of the frame. This will be your lacing board.
Centre your fabric over the lacing board. Attach it to the board by pushing pins through the fabric into the board along the top edge.
Pull the fabric gently, make sure that it's straight, and pin along the bottom edge, then repeat for the two sides. Keep checking that your fabric is straight
Thread a needle with strong cotton and knot the end. Turn the picture over so that you're working from the underside, and lace from top to bottom with an under-and over motion. Start at one edge, stop half way and repeat from the other side. When you reach the centre, tighten the cotton gently to remove the slack and knot the ends. Repeat with the other two edges. You can join in a new piece of thread by tying it on with a reef knot.
Stitch the corners in place, remove the pins, and put the picture in the frame.
Good luck.