For setting temperature using web interface you need to use our applications on printer page: Joystick or Console.
In first application you just need to go to extruder menu, write temperature and press set. Here, in right top corner, you could find current temperature and position of your bed and extruder. Moreover, in this application you could easily change position of your extruder and see this in units and camera.
If you will use application "Console", you need to write next command: M104 S55. This command will set temperature to 55 degree.
Software engineer, 3DPrinterOS