In theory, it's simple math:
33 / 45 = 0.73
So 33rpm is 73% of the speed of 44rpm, and vice versa. How this translates to the pitch control on a turntable, dunno - I'm not a dj. But if you have an audio editor such as SoundForge, it's easy enough to calculate how much longer the slower version should be, and enter those values in there...