Use TotalCommander.
Open (enter) data.zip. In folder ui_android, subfolders 800_480 and 800_480\skin_night, delete loading.bmp files.
At same places, put your loading.bmp. Your files must be same format (bmp)and resolution (800x480).
This is if your navi is Android based.
If it is working on WinCE, same procedure in data.zip, subfolder ui_igo9.