After downloading the .zip file, right-click it > Properties, and cick the Unblock button.
Unzip the file.
Rename your \Plugins\Shipping.UPS folder (e.g. Shipping.UPS.Old)
Copy the Shipping.UPS folder from the .zip file into your \Plugins folder

Upgrading to new version of UPS plugin... 
Use this trick to quickly (save) re-enter your existing configuration: 
1) In browser, go to UPS's Configure page. (We'll come back here later to re-"Save" these settings, but you should write down or screen shot just in case)
2) Then go to Configuration > Plugins, and Uninstall UPS 
3) When it comes back, Install UPS 
4) When it comes back, use browser back button to get back to the UPS Configure page - all your settings should still be there. Just click the Save button. 

P.S.  If you will use Packing Type "Pack by volume", you will need to enter 5184 in Package volume" field, since it was not present when you clicked Save in step 4 above, and thus overwrote the installed value with 0

Warning: Do not enable Tracing unless you are trouble shooting.   Every request and response XML will be logged to the System Log (including AccessKey/UserName,Password). Do not leave this enabled in a production environment.