sudo nano /etc/hostname
In the resulting editor, change “osmc” to whatever name you want. Then ctrl-x and y to save.
sudo nano/etc/hosts
Same here, change both instances of “osmc” and exit/save as above.
You will have to reboot your pi for these changes to take effect.
In the meantime, I’ve made a post that includes some linux command cheat sheets/guides and general linux tutorials that would likely be helpful for you.