First you need to uninstall Sortd, though you don’t necessarily need to revoke permissions unless you want to, but it is recommended. See How can I revoke Sortd's permission to access my email?.
You should then clear all of your Sortd cookies by following the instructions here.
You can download Sortd again here.
Note: It is highly recommended that you close any Gmail browser tabs once you have uninstalled Sortd before installing the Chrome Extension again.
In general you should never have to re-install Sortd. When we update the Chrome Extension, the Chrome Browser will automatically download and update it. Unfortunately however, it will not update Sortd in any open tabs which Sortd is running in, without a full reload of the tab, and or closing the Gmail/Sortd tab and opening a new one. Additionally Chrome decides when to download the updated extension, so we cannot control when it will happen exactly.
Under most conditions you should not need to worry about any of this as if Sortd sees that the Chrome Extension has updated but it is not running the latest version in your Gmail/Sortd tab, it will notify you and ask you to reload the tab. Under certain conditions where the the new Extension is not backwards compatible it will force you to do so and disable itself until you have done so, so as to ensure you do not lose any data.
The re-install is only necessary if something has gone wrong, or there is a clash with other Chrome Extensions.
We often release Bug Fixes which do not require updates to the Chrome Extension and a simple browser refresh will ensure you have the latest version, so it is a good idea to refresh the tab from time to time, if you leave it open generally, and/or if you are experiencing issues.