The version 5 is particularly desirable since a new layout engine for the dashboard has been developed, and is quite powerfull !
So to update your install of Grafana from 4 to 5 you need to launch several command with root or a privileged user.
The service should automaticly restart when the update is done , but check that it is running with :
service grafana-server status
You should see something like this
? grafana-server.service – Grafana instance
Loaded: loaded (/usr/lib/systemd/system/grafana-server.service; disabled)
Active: active (running) since ven. 2018-04-20 17:47:41 CEST; 1 day 22h ago