Yes, you can remove IPs manually VIA command line. Before you remove your server IP you should know that DA will not function, because it is licensed by IP.
If you are renting your DA license from a service provider ask them to change the license to the IP you would like to use, or if you bought it from DA contact their sales department.
How to remove the old IP:
1. Login as root to your server
Change to the IP directory
# cd /usr/local/directadmin/data/admin/ips
Remove the old IP
# rm -rf 18.104.22.168
Make your new IP the server IP
# vi 22.214.171.124
Use "i" to insert/edit.
Once you have finished your edit press the "Esc" key.
Then write and quite with this ":wq" then press "enter"
Make it look like below. You will assign the user and ns through DA.