You have to 'get root'
then add the group "sudo" to yourself
usermod -a -G sudo <yourusername>
while you are at it, add the group "adm", this will allow you to read logs without getting root.
it is best to edit that with, as root
that 'editor' will check the file before committing it.
If you 'mess up' /etc/sudoers on a system that doesn’t have a standard root account you can lock yourself out of root.
Alternatively, use the GUI "Users and groups" ( found in settings ) and change the account type from standard to administrator
You will either need root password, or use the already privileged account.
Since Ubuntu doesn’t setup a root account by default, the latter is the way to go.