Here is a step by step guide & with screenshots about how to remove "Powered by Shopify" if you don't want it to appear on your store.
1- From you Shopify admin panel go to Online Store > Themes > Actions > Edit Languages.
2- In the Filter translations box, type "powered".
3- In the Powered by Shopify box, use the space bar on your keyboard to type a single space.
4- Click Save.