You cannot make changes directly to your Knowledge Panel. Once you have claimed the Knowledge Panel, you can ask for changes through the feedback button situated in the bottom right hand corner. A Google employee will assess your requests and apply it if they judge it to be accurate and helpful.
At Kalicube we have developed techniques to change information indirectly by updating information around the web about the entity (in this case lawyer). Using the Kalicube Process, you can have control over your Knowledge Panel.