Hank here from Shopify!
While it is not possible to change your .myshopify.com store URL, there are still some things you can change, like your store name and you can buy a custom domain. I will share more information on both below!
The first step if you want to is, you can change the name of your store in Settings > General. As mentioned this will not change the URL that you have, but it will change the name of your store and how it appears.
Then another option you have is to purchase a custom domain. Purchasing a custom domain allows you to have the domain that you want, and it really strengthens your brand online. I will share a video of the process below, which can be found in your admin by going to Online Store > Domains.
Let me know how you get on with this, or if you have any further questions for me!
All the best,
Therere's a 'Store Name' field at the top of the Settings > General page. Update that and save.
For the domain, go to Online Store > Domains and connect a new domain.