A wheelchair having a lower frame with drive wheels and forwardly extending arms with casters and an upper frame with a seat and backrest. Linkage assemblies on opposing sides pivotably attach at a first end to the lower frame and at a second end to the upper frame. Power cylinders attached on opposing sides are extendable between the upper frame and the lower frame and are lockable from moving from a selected position. When unlocked, the power cylinders apply a supplemental force in association with a force applied by a user on the drive wheels for moving the upper frame relative to the lower frame guided by the linkage assembly. A method of adjusting the seat height of a wheelchair is disclosed.