HOWTO Change the MX record of your website
I Will Expalin Basic way And Advanced Way
First Basic way (If you are not a server administrator )

you can only add one mx record and can't set any type of priority on it, secondly you cannot set a MX record as an IP address. You'll need to contact the admin once again. Otherwise go to Cpanel, Mail, MX record and enter the full domain of the server you want mail to go to and it will do the rest

Second Advanced MX Changes - CHANGE TO IP ADDRESS
1) Login to the server WHM as the root user.
2) Go to DNS Functions and Edit DNS Zone
3) Select the domain you want to edit, or type it in, and click on Edit.
4) You should see the following, or something very close to it:
5) Now the MX has a priority of 0 meaning its the only MX entry used for the domain. Replace the domainame.com. with mail.domainame.com.
6) Now change mail from CNAME to A record and take out the domain, and replace it with the IP address.
7) Save the changes. Bind will reload, if it shows any errors then you did something wrong, make sure the MX entry has a . after it!
8) Login to your server by shell as the root user. Edit the /etc/localdomains file
pico /etc/localdomains then ctrl+w to and type in the domain you modified.
Delete the entry for the domain.
Save the changes to the file, ctrl+x then
Y
9) Edit the /etc/remotedomains file - this tells Exim to not handle mail for this domain.
pico /etc/remotedomains
Add the domain name to this file.
Save the changes.
10) Your now done! Make sure you dns is updated, in shell run:
host -t mx domainname.com
You should see mail.domainname.com