Originally Posted by Trotter
I have always used TeamViewer. You can use it for free as long as it is for non-business. Send him the file for it and talk him through clicking through on the non-install version. Once you connect you can install the regular version and set it up so you can access it when you need to.
I'll add onto this: Have him download the "Quick Connect" version. It's an executable that he just runs, and it pops up a window with a username/password. Then you can use the full install of Team Viewer to connect with the credentials he gives you. And anytime he needs your help, he can just run that file and you can connect.
An alternative, is if Chrome is installed on his system, you can use Chrome Remote Desktop, and set it up so you can remote into it anytime.