License: Free for personal and commercial use with attribution. 
Include visible link to https://whcompare.com, preferably on the same page where used, alternatively on another page or in the code.

If you want to share these icons for download on another website, you are free to do so, as long as you inform about the license and that attribution is required.
Also link back to https://whcompare.com on all pages where the icons can be downloaded.

If you have made changes to the icons before sharing them please inform about that at the same web page that you share them. 
If you have made changes to the icons and make them part of a greater design like a web design theme website design this you do not need to inform about changes.

The icons can be freely used on website designs and web design themes available for resale or free redistribution.
Then, however, attribution is required either with a visible link back to https://whcompare.com, alternatively with a notice in an attached readable file or in the code.