The frequency you send on doesn’t set speed, frequency determines things like the waves spread / go through solid objects etc. ie 434 should go through walls better
To increase sending speed in LoRa you need to use wider channels, less spreading, chip codes etc. so more of what is sent is data and not spreading. I expect these will be set to some default
in a header file that needs to be edited or new values set. Sending faster will probably mean sending less distance. If you need the range then you may have to change program to send less often so you don’t use up your duty cycle allowance.