Via the CLI:

root@tom-G73Sw:~# cd /etc/netplan/
root@tom-G73Sw:/etc/netplan# cat 01-network-manager-all.yaml
# Let NetworkManager manage all devices on this system
network:
version: 2
renderer: NetworkManager
ethernets:
enp5s0:
dhcp4: no
addresses: [192.168.0.15/24]
gateway4: 192.168.0.1
nameservers:
addresses: [192.168.0.224,192.168.0.46,192.168.0.51]
root@tom-G73Sw:/etc/netplan#

Then issue:

netplan try

so changes take effect.  Via UI, go to Activities then Settings, select Network or WiFi, based on which interface you wish to set the IP on.  Typically leaving the WiFi as DHCP might make some sense for redundancy.  Your choice:

Ubuntu Static IP Configuration via GUI

Cheers,