Generally, IME upgrades are easier mid-week. But, at times weekends are easy too. E.g. I happen to look at SA/SU 12/13 westbound. SA even had NC=2, XC=2. Both days are only about 50% booked. Summer vacation time often shows low premium cabin loads too. Bottom line: not the easiest but definitely doable.

@ OP: How many weeks out are you travelling?