After you adjust the steps/mm power cycle the printer to make sure it's saved permanently. I think by default it only changes it temporarily and you have to do some kind of save operation. Although maybe it *does* save it. Anyway if you have questions about that post them here and I will answer or tinkergnome himself will answer.
Yes. The firmware is here. You can always go back to the official firmware. So install tinkerMarlin:
Get the only one that matches your machine. From your description it would be near the end of the list. It should *not* say dual. It should say "plus":
The hex file is the firmware. Then you connect a USB cable from your printer to your computer. Then you have many options on installation. I'd try cura first although it's the most likely one to have trouble seeing your printer. In Cura 14.X or 15.X it's pretty easy. In latest cura do PREPARE mode, then click on the printer drop down and then "manage printers" and then UPDATE FIRMWARE and then custom firmware option. Often it can't see your printer for a few possible reasons. You need the USB driver which should be bundled with Cura. At least it used to. On windows you can check if there is a com port in device manager that is added when you connect the usb cable. You can connect and unconnect a few times and you should see a COM port added. In the old days it was like COM3 but now typically it's a larger number like COM17 and cura doesn't look that high I think. So if you see the COM port in device manager but not in cura then you need different software. You can google about how to install firmware for arduino (as it's an arduino computer inside the UM2+) and there's tons of help for you there. Or use printrun software here:
Which should have less trouble connecting to your printer and installing new firmware.
Once installed the rest is easy - find the steps/mm settings for all 4 axes and if your cubes are say 5% too small than increase steps/mm by 5%.
Et si tu recherches la valeur "cool" dans les paramètres ("Search settings"), tu dois voir apparaitre le paramètre "Minimum Layer Time" dans "Cooling", certes, en grisé mais modifiable.
Et si tu cliques sur les réglages pour "Cooling", tu pourras cocher l'option pour qu'elle apparaisse dans tes réglages "utiles".
Mais il faut être en "Custom Mode", du coup...
Hey, here the result for me trying this solution.
After adding this content to my .cfg file as described:
machine_disallowed_areas = [
I got the following result
Hope this will help ;)