How to give remote support to parents?

I live in a different country than my parents but sometimes I need to help them out with computer issues. Doing this over the phone is a massive pain and it would be great if I could remote into their machine in order to do what is necessary. What is the easiest way to set this up? It would need to be easy enough for them to do it on their end, since I won't be able to do it for them. Also, since I only need to do this a couple of times a year I don't want to pay for a service that requires a monthly fee (e.g. GoToAssist) since it just wouldn't be worth it for me. Though I don't mind a small once-off cost.

What do you use for remote tech support?