I am trying to replace the ink cartridges and the

Dont worry about that., for you to make it stop the printhead on the center

heres the thing you need to do:

You will noticed that every time that you open the printer access door the pritnhead will move and most of the time it will stop on the middle right?

Now If you see your printhead its move onto the center immediately unplug the power cable of the printer to cut off the power and I Assure you your printhead will remain on the center. don't worry it will not cause any problem on your printer by doing the troubleshooting., Gudluck!