Login to your local store merchant account at: https://merchants.shoptoit.ca/
Click on 'Business Information' either on the left hand menu or on the main screen.
Then click on 'Enhanced Information'.
Scroll down to "Store Description".
Fill in or change the text field. You have a maximum of 32,000 characters to describe your store and what you do. Don't be shy explain what you offer and why you are the best. :-)
Scroll to the bottom of the page and click on 'save' to save your changes.