Many times after a knee surgery, or even with knee osteoarthritis, people have a hard time getting their knee extension back. Being able to straighten out your knee is very important in many things we do, especially walking.
To start off, you can try chair props. Sit in a chair, and have something of equal height in front of you. It can be another chair, an ottoman, etc. Place your heel on the other chair, and try to straighten out your knee as much as possible. If this is not enough stretch, you can add weights to it. A sack of potatoes works well, but sometimes it is too much weight to start with on your leg. Get a plastic bag, and add some soup or vegetable cans to it. Slide your foot through the loop of the bag, and place it just above your knee. Try to hold it there for 5-10 minutes and relax as much as you can. Over time, you can add more cans of soup.
If you need more of a stretch, you can lie down on your stomach on the couch or your bed. Make sure your knee is hanging off the edge to help you get more of a stretch and take the pressure off your knee. Sometimes you can roll up a towel and place it under your thigh for comfort, and more of a stretch. If this is not enough stretch, you can add weights to it. Get a plastic bag, and add some soup or vegetable cans to it. Slide your foot through the loop of the bag, and place it at your ankle. Try to hold it there for 5-10 minutes and relax as much as you can. Over time, you can add more cans of soup.