Agreed with Sahara. Start your cues as light as you would prefer the horse to respond to, and escalate until you get the desired response.
For an upward transition, think forward (making sure that you aren't blocking her with the reins), close your legs, squeeze, cluck/kiss, and then spank with rhythm until you get the transition. When the horse responds, let your aids go neutral. Be very consistent and clear in the application and the release of the aids - the horse learns from the release, not the pressure.
For a downward transition, think about slowing down (exhale, slow your seat, close your legs and "melt" into the tack), and back up the seat/leg aids with a verbal "whoa" and a closing of the hand (no pulling, just closing the front door).
Horses typically aren't truly lazy - they can be very dull to the aids, and it takes consistent clarity to build or restore that "Yes'm/Yessir" response. It may take more than 4-5 weeks, depending on the horse. Don't rush his progress for the sake of an event - take the time it takes and build a good foundation, and you'll have a better partner faster for it.
A stubborn horse walks behind you, an impatient one in front of you, but a noble companion walks beside you ~ Unknown