Here is the link to the upgrade chart:
http://www.miles-and-more.com/mediap...1536550819.pdf
Depending on the booking class of your eco ticket you need 35000 (B,Y) or 50000 (other booking classes) miles.
Be aware that some very cheap booking classes are not eligible for upgrade (edit: E, K, L, T).
Call LX in BSL, tell them on the phone you would like to upgrade, give them your booking code and they will check if upgrade is possible. Have your M&M pin ready for identification.
I did this twice last week (for upgrade from C -> F). Was really easy and fast.