I'm collecting what I've learnt over the past few days, in the unlikely event it helps someone else...

How to upgrade with miles on Saudia

(This is for international travel to Europe, US etc.)

1. Book and ticket the flight you want to pay for. For Economy, ensure this is in Y, B or M classes only. (For Business, J, C or D classes only). You cannot upgrade from Q class or below. You cannot change class by paying the extra - you would have to rebook.

2. Book flights in D class (for Y-J upgrades) or A class (for J-F or Y-F upgrades). Note these have to be the same route, but do NOT have to be the exact same flights. You need confirmed bookings - if you're waitlisted, you're probably sunk.

3. Fax or email the Al Fursan centre the following:
- Ticket number and PNR number of the lower class booking
- PNR number of the higher class booking
- Al Fursan membership number
- Where you want to pick the tickets up from

4. Wait. The faxes and emails are collected once a day from the communications centre and taken to the upgrades centre. The upgrades centre only works a few hours per day - either from 9-12 or 10-2.30 depending who you ask. They will probably lose your fax or email a few times.

5. Keep an eye on your higher class booking. It'll probably expire before they process the upgrade. If this happens, rebook and call them to tell them the new PNR.

6. Hope.

I've been fighting for three days and they have not yet got round to processing my upgrade. I will update this post if they manage...