There are two important considerations before approaching the firmware issue: first, do you have an all-metal, direct-drive extruder? If you don't, your Bowden tube will melt where it enters the hot end and lead to clogs before you ever reach 300 °C (the same may be true of other plastic parts, if present). Second: is your heater cartridge rated for high ...
I wanted to expand on the great comment by 0scar and explain what's the fastest way to change pins. I know this is an older topic, but for the sake of people looking for an answer, I figured I add this.
First of all it's easiest to change the pins in the pins file for your specific board by simply renaming E0 to E1 and vice versa. This is much simpler than ...
Enabling ADVANCED_PAUSE_FEATURE requires a rebuild and upload/install of a new Marlin firmware. The option is found in the advanced configuration file (Configuration_adv.h).
Rebuild and install the firmware.
I think you might be asking how to adjust your steps per mm, but if the motor is moving the correct distance, but at a slow speed, then it might just be a speed problem with settings, or whatever it might be. I have an Ender 3 but I think I might be able to show you how to calculate the steps per mm. There is a simple equation for this.
New E-steps=(target ...