Step1: Login to your Shopify account. When you log in, you will see the Home page of your store.
Step2: There is 'Settings' placed on lower left corner of the screen. Click the 'Settings' button.
Step3: Choose 'General' option of the Settings
Step4: You will see your store name on the 'Store Details' box of General Settings.
Need more? Go to Shopify Help.