Sorry, been on the boat for a week.
Your controller will easily handle a 48v conversion without changing too much.
You will need a 48v solenoid or you can short wire the 36v solenoid.
If you are planning on 6x8v batteries you can wire the solenoid to the 5th battery and run the solenoid on 40v. If your plan is to use 8x6v batteries, just wire it to the 6th battery at 36v.
You will also need a method to charge 48v.
The wiring diagram for your cart is the same as the old Ezgo Marathon