A few weeks ago, I decided to change the default osmc password to something more secure. Of course I managed to forget this secured password. Fortunately for me there is a way to reset it without damaging anything.
Stop your raspberry
Remove your sdcard and plug it in another computer
On the sdcard edit the file cmdline.txt
Write init=/bin/bash at the end of the first line
Save the file and plug back the sdcard in your raspberry
Power the RB and Run passwd osmc
Change your password
Remove init=/bin/bash the same you used to write it in the cmdline.txt
Et voilà
Have fun.