Tiers 11, 12 and 13 troops can be enhanced in the Family Advancement Center using Family Hi-Tech Parts. Family Advancement Center is unlocked when your mansion reaches Elite 5. You can further enhance T11 troops in Legacy R&D Center (unlocked at E6+10%).
Enhancing T12 troops requires the Family Training Center to be at least level 10.
Enhancing T13 troops requires the Family Training Center to be at least level 30.