I've tried to upgrade it using United miles and have failed. It is not a recognized class of service, as it relates to M+ awards and upgrades.

However, if you have Turkish miles, you can upgrade according to the chart in the link below. I didn't explore the possibility of transferring from M+ to THY. You may want to see if this is an option, otherwise you'll be in economy or bump up to business.

http://www.turkishairlines.com/en-IN...ade_tablo.aspx