Open a terminal emulator like xterm, type "regedit" and press enter.
Then just follow the path and when you are on the desired location, right click the white space on the right-most part and select from the menu the option to create a new string. Give to the string the desired name (UseDGA) and press enter to create it. Then double click it to assign a value, in this case "Y".
That should be easy enough, another question is if that will help you with your problem. I can't answer that.