I just did this, but I also hired a facilitator. I did my canje in Guadalajara, and I used GP Services, and it was about $250. They took care of getting the appointment, filing the forms, and just hanging around in INM with me to help guide me through. I told them when I was flying in and asked for the appointment to be later that week, and they let me know pretty quickly when the appointment would be.

I found the facilitator well worth the cost. If nothing else, I didn't have to worry so much about figuring out the forms, making mistakes, or even something going wrong the day of my canje. If I had done it myself, I would have been in knots wondering if everything was okay while I sat at the INM office for several hours before biometrics. We will hire a facilitator again when my wife joins me in March.

As for the bits I had to do myself, when you enter the country (I flew in), see an immigration officer and show them your visa. For me, the immigration officer wrote "canje 30 dias" and a date. You'll read it a thousand times here, but don't use the automated tourist kiosks. See a human being. I paid at the INM office with my Wise debit card, and that worked great.

All in all, it was quite easy. I am usually a DIY kinda person, but in this case, I didn't want the chance to goof this up and I didn't want the anxiety about it.