Go to Customize > HTML
Copy this code then in the HTML document find <head>, use CTRL + F, paste code right under the <head> line. In the begining of the code you can see a green text that says:
controlHTML: ‘<img src=”YOURIMAGEURLGOESHERE” width=”100″/>’, //HTML for control, which is auto wrapped in DIV w/ ID=”topcontrol”
Replace the bolded text with the url of your image, like i did in the picutre below.
Save the file and that’s it! You will have the BACK TO TOP button.
On this page you can find some nice pictures for your BACK TO TOP button.Feel free to post your custom images in the comments below.