Kill off Kim Il Sung's entire bloodline, so the whole connection between the people and the "Eternal President", is severed for good.
Start purging Kim's inner circle, top party officials and upper echelons of the military, since they'll most likely oppose any reforms. Put on kangaroo courts, and send them too one of North Korea's many "summer camps". All the dirty work has to be done real quick and clean, so a messy civil war is avoided.
Start amnesty of all political prisoners in phases, do it all at once and you'll have chaos on your hands.
Sign a Non-aggression treaty with South Korea, and drastically cut the military budget since most of aid the north gets, goes to the military, while everyone else starves. Don't totally disarm, because theres plenty of old guys in high places down south, that still have axes to grind.
Abandon the nuke program, the powers that be will be all to willing to drop crippling sanctions, hopefully.
Lastly, copy and try to implement every market reform that Deng Xiaoping did in China.