Yes you can use ROP miles for an LH upgrade:
http://thaiair.com/Royal_Orchid_Plus...r_Alliance.htm
You need to calculate the distance you will travel each way - this could be useful:
http://www.airtimetable.com/Air_mile_calculator.htm
You have to get Thai Airways to do the booking, but I would highly recommend you check out the competence of the local office. In Kuwait for example, TG sucks and made mistakes on my awards booking before. I had to get LH Kuwait to sort it out, PLUS make a trip to Silom TG to verify.