Use the Search box to find all the Joes Shoes transactions. Click the Cateogry column to sort them by Category. Select the first one in the “Clothes” group, and Shift-click on the last of the “Clothes" group so all those transactions are highlighted. Then select Transacitons > Edit Transaction, enter the category of Shoes, and press okay. Finally, click Clear filters and click on the Date column heading to re-display all your transacitons in date order.
For the future, you want to create a QuickFill rule to tell Quicken that when the Payee is Joes Shoes, the Category should be Shoes. Post back if you need help on how to do that.