Edit the file /etc/sudoers and add the following line. Replace username with the username you want.

# User privilege specification
username    ALL=(ALL:ALL) ALL

/Pargorn

Update on 20191014

We can make the access even more permissive by specifying

username    ALL=(ALL:ALL) NOPASSWD:ALL

After this, it is likely that you will forget your password soon! ;-P

/Pargorn