This requires some technical knowledge and front end development from a web designer.

Go to Storefronts
Now create a new storefront for testing purposes
Go on SAYL to Settings, then go to the URL builder (make sure you select the test storefront)
Add ?nocache=1 to the URL to clear the cache
Now you can let the designer work his magic (inspect,...)
Paste the text you want to change in the testing SAYL storefront like this:

This is now overwritten in SAYL.

For inspiration, visit the Take Away site of Ellis.