If you are quitting SquareSpace to join PhotoFolio, Welcome! Some photographers purchased a domain with their site and wondered how to move it to our service. Luckily they have a guide to help you with that: https://support.squarespace.com/hc/en-us/articles/205845348-What-to-do-with-your-domain-if-you-cancel-your-website
It's very simple to keep paying for the domain there and point it to us for your website needs.
NOTE: SquareSpace is a domain reseller and you may find a better deal by moving the domain to a registrar like: https://www.hover.com/