The method of comparing two versions of the same thing to see which one converts at a higher rate is known as A/B testing or split testing. Almost anything can be split tested, but the most common items are headlines, sub headlines, paragraph text, images, testimonials, calls to action, links, and social proof content.
To run a split test, do the following:
Isolate one variable.
Make two identical items, with the exception of the isolated variable.
Test both items on the same number of people.
See which converts at a higher rate. Use that one, and test other variables if interested.