The easiest way to transform your existing desk into a sit-stand desk is to use a Sit-Stand Converter.  They are easy to use and placed on top of the desk.  It come straight out of the box and only need to attach the keyboard tray to the converter. There are many different types and sizes for many different applications.  Pick the right one for you with the size you need and the size of the desk you will place the converter on.  Most users pick a converter because they don't want to buy a new full-size desk and they want to keep their existing one.