Hello, We are planning to change our ip address of our server. So I wanted to ask how can I do that without removing it and adding it again, becouse I will loose my rank.

If you have claimed your server, you have the ability to set a DNS address for the page. You can use that, and change the IP it points to when you need to and GT will update the page. For this to work it needs to be the same ports.

If you are unable to do this, you'll have to re-add the server and wait just a week for rank to get back since that's all rank looks at.