Transfer Tool: The source server is not running the same major version as the target server.

Symptoms

When using the Transfer Tool, the following warning is reported:

The source server is not running the same major version as the target server.
cPanel highly recommends that the source server runs the same major version for
at least 24 hours to ensure any data conversions have completed.

Description 

This warning is reported when the cPanel version on the source server is older than the cPanel version on the destination server.

Workaround

Update cPanel on the source server to the same version on the destination server.

How do I update the cPanel & WHM software on my server?

If it is not possible to update cPanel on the source server, proceed with performing the transfer.