The Fire comes with Quickoffice pre-installed and there doesn't appear to be any way to remove it even if you have Quickoffice Pro installed.
If you open the pre-installed version of Quickoffice there is an option to update. Pressing this button and clicking Buy Now will take you to the Amazon App Store. Since you've already purchased Quickoffice Pro it will have an option to Open. Doing this does nothing to "update" the pre-installed version and doesn't remove it.