Metamorphic to Igneous: Melting and Cooling
Metamorphic to Sedimentary: Erosion and Deposition
Igneous to Metamorphic: Heat and Pressure
Igneous to Sedimentary: Erosion and Deposition
Sedimentary to Metamorphic: Heat and Pressure
Sedimentary to Igneous: Heat and Pressure
I am so sorry if I got it wrong, sometimes I forget the rock cycle. Most likely Sedimemntary to Igneous is wrong.