IP Address Change Notice

I have a dedicated server using virtualmin panel.
I got a notice that I was required to change the ip on my server.

for example like this:
Old IP address: 123 111 111 111, 123 111 111 112

New IP Address: 123 111 121 111, 123 111 121 112
New IP Subnet:
New IP Gateway: 123 111 121 201

so I want to login webmin like this:
Old url:
New url:

How can I change it in virtualmin?

how do I change it safely? because it contains a lot of our clients website.

Thank you so much and I really appreciate your help.