[runnoahrun]

If my current controller is rated at 6A per phase and I wanted to increase that to something like 15A could I swap out the MOSFETs for higher rated ones and put a better heat sink and fan on them? Or is there more to it than that?

[ViperTX]

If the replacement MOSFETs have about the same gate characteristics then you should be able to exchange them. You also must make sure that you replace N Types with N Types and P Types with P Types. You may also run across the logic type FETs, so be aware. Also make sure that the package types (T0220, etc.) are the same or at least exchangeable (Things like Pin1 is Gate, Pin 2 is the Drain, etc.).

[Al_The_Man]

The other thing maybe as the current will be quite a bit higher is check the wattage rating.
Al

[H500]

The voltage must be equal or higher also. The circuit board traces might also need to be beefed up. The current sensing resistor might need to be higher watt.

[ESjaavik]

Yes, there is more to it than that. If you need to ask, you should not do it.

If you are able to design it from scratch, then redesigning may be an alternative to save you from making a PCB yourself. In an existing design you should even be careful changing to the same type from another manufacturer.