What is your goal here, you already made it up the hill? If you want to climb the hill faster it will be harder. If you want to make it easier for yourself go slower, especially at the beginning when it is less steep. So shift down early (meaning that as soon as you feel the effort going up too much to remain at a high cadence you shift to a lower gear), keep spinning and remain seated. At some point you reached the lowest gear, then start lowering your cadence in order to keep the effort at a minimum. At some point the cadence is too low to remain seated and you have to stand, this is what you have been holding back for and now you can just stay seated at this minimum cadence until you can not hold it anymore and then finish it off standing.