You can modify the entries inside an SPF record from inside the cPanel interface. The changeable entries include the following:
Additional MX Servers
Additional IP Address Blocks (IPv4)
Additional IP Address Blocks (IPv6)
Include List (INCLUDE)
Exclude All Other Hosts ("-all" Entry)
1. Log in to the cPanel interface for your domain.
2. Navigate to the following location:
cPanel: Home -> Email -> Email Deliverability
3. Locate the domain to modify, and click "Manage".
4. Locate the SPF record on the page, and click on the 'CUSTOMIZE' pencil icon.
5. This will take to the 'Customize an SPF record' page.
6. Below, you will see the options to add or remove the values in the SPF record.
7. View the preview of the modified SPF record below.
8. To finish, click the "INSTALL A CUSTOMIZE SPF RECORD".
This interface will make the SPF record change permanent as well.
To learn how to customize the SPF record by command-line, click the following article: