How far does the swelling spread up the leg?
Any change to color or temperature of the leg?
How much bigger is the worst foot?
If you have swelling of ankle and feet then you need to have a check by your doctor.
There are a variety of reasons for swollen ankles and feet including high blood pressure, cardiovascular problems, circulation problem, kidney problem and something putting pressure on a major vein (the Inferior vena cava)
Transient swelling could be related to prolonged immobility causing calf muscles failing to pump fluid back into the circulation. Other causes include varicose veins, side-effects of some drugs and being overweight.
A mild diuretic would be the first action, together with compression hosiery.
Keep your legs elevated at a high angle when you can to encourage drainage and if you have a sedentary job ensure that you get up and move around every hour.
Avoid caffeine drinks, but do continue to drink water. Reduce your salt intake too.
If the problem was just on one side, or there was a history of trauma then we might think of a sprained ligament however I think this is more of an edema problem.