How to remove a systemd's service?

Disabling a service from systemd:

To disable a systemd’s service the following command can be used:

systemctl stop service-name; 
systemctl disable service-name;

Removing a service from systemd:

Systemd uses unit (file to define services) to remove a service the unit file have to be removed, here is a list of unit locations:

/etc/systemd/system/ (and sub directories)
/usr/local/etc/systemd/system/ (and sub directories)
~/.config/systemd/user/ (and sub directories)
/usr/lib/systemd/ (and sub directories)
/usr/local/lib/systemd/ (and sub directories)
/etc/init.d/ (Converted old service system)

Refresh/Reload systemd:

systemctl daemon-reload
systemctl reset-failed

Ghost services (not-found):

Systemd can list ghost (not-found) services even if the unit is deleted for many reasons

1. Unit still present on one of the systemd directory
2. Unit does not exit but a file link is still present on one of the systemd directory
3. The service is used in other unit(s)*

(*) if a service is mentioned in other unit but does not exist systemd will still list that service with the state not-found even if there is not unit file… you can search what unit is using that service with a text search and edit those units (not recommended if you plan to install that service later)