Users and groups

I think it is a good practice to switch to different user account and get rid of the standard pi one.

Adding new user

sudo adduser max

If you were not prompted for the password or if you want to change it later

sudo passwd max

Adding user to sudo group

sudo usermod -aG sudo max

Deleting user

sudo userdel -r pi

The r flag causes deletion of home dir and mail spool

Adding group

Adding this just for reference

sudo addgroup media
sudo usermod -aG media max