If possible, secure the strut in a vise, which will make for an easier installation. Don't clamp down on the strut housing, which will damage internal components. With stock springs, use an external spring compressor to release the spring force on the upper strut mount assembly. The Maximum Motorsports test car had aftermarket springs, so the shorter spring didn't need to be compressed. Either way, remove the upper strut-retaining nut (and washer if present) as shown, while holding the strut shaft with the correctly sized Allen socket.