What you are describing sounds like dependent edema. In your case I think it is caused by venous insufficiency, which causes blood to pool in your legs and fluid to seep out into your tissue. When you are sitting, the blood coming from your lower legs has a hard time getting back to the heart. As a result, some of the fluid must leave the veins in the lowest part of the legs. While lowering your salt intake is almost always a good idea, it is only likely to have a small effect on your leg edema (but a good thought). Perhaps the best first step for you to take is to spend less time in your chair in front of the computer. You could start by standing up periodically and walking around the room to get your blood flowing. Another measure you can take is to wear compressive stockings, or T.E.D. hose. The compression around your lower legs will prevent this fluid from leaving your veins and causing the edema.
I should say that since lower limb edema can be a sign of other diseases such as heart disease, liver disease, and kidney disease, you should be evaluated by a physician before starting any therapy yourself. The best type of physician for you to see for this problem is a primary care physician
such as an internist