On the the login page there is a container on the left side prompting the user to register if they have not. The text is:
"By creating an account at nopCommerce you will be able to shop faster, be up to date on an orders status, and keep track of the orders you have previously made."
Go to admin section > Content Management > Localization
Select Language English
At the bottom of the page you will find "Login.NewCustomerText" - > It must be difficult to find this in a big list of stuff there, simply Ctrl + F and search for "By creating an account at nopCommerce"
You will see this:
Resource Name Resource Value Login.NewCustomerText By creating an account at nopCommerce you will be able to EDIT shop faster, be up to date on an orders status, and keep track of the orders you have previously made.
Click on EDIT
There you can change the "Resource value:" and you can write whatever you want with your store name