Yes You Can Change Your Facebook Cover By This Site By Free Way and Here's The Steps to Change Your Facebook Cover:
1- Open The Following Site http://covermyfb.com/generator/image_uploader

2- Start 1st Step (Create The Background) Then Upload The Image You Like to Make it as Background and Chose The Size of It

3- Then Press Preview to See View of Banner

4- Then Chose The 2nd Step (Write The Text You Like) You Have to Write The Text and Chose The Font and The Font Color and The Effect and The Color of Effect and You Can Move Your Text to The Area You Like in Your Background Then Press Preview to What You Did.

5- You Can Write Up to 3 Lines in Your Banner.
6- You Can Also Add A Border to Your Banner.

7- Then Press Save to Finish Your Cover
8- Then Chose The Type of Watermark and It's Place on Your Banner