Whether it's converting from natural gas to propane or the opposite, in both cases the 1st step is to change out the gas orifices. The gas orifice is a small hole at the end of the gas valve where it connects to the burner. These can be unscrewed using a wrench.
To access the orifices, step 1 is to remove the burner by lifting it up, then towards the back of the grill. In the hole the front of the burner was in previously near the front of the grill, there will be the burner valve and orifice. Unscrew the old orifices from each valve and replace them with the ones provided in the conversion kit.
For rotisserie orifices, remove the back panel of the grill. After it is out of the way, there will be direct access to the orifice.
After these steps, the regulator on the back of the grill will need the cap to be unscrewed and flipped. This can be done with a screwdriver or a coin. It says either NG or LP on the side of the cap, NG for natural gas and LP for propane.
If converting to propane, a hose was included in the conversion kit. This is also attached here to this regulator.