Bigcommerce Extreme Price Increase - Instruction on moving website domain?

6 months ago I was notified that Homestead's storefront would increase significantly ($500 a year to $4,250 a year).  I started working at that time to migrate my store to a better format (I had held back as I don't like change but I liked what Shopify was offering)  that would support my sales at a lower cost.  My Shopify account is ready to open up but I would like to migrate my website address to that site as Homestead does not seem to support implementing Shopify into their platform.  What steps are needed to moving my website address?  Sad to leave Homestead as I've been with you for over 20 years but I can't support a price change that was implemented by Bigcommerce for a simple online sale site.  (My sales for the site are less than $500 a year but I sell across Amazon and Ebay and need the site to support customers coming back to reorder and the integration to synchronize my inventory).