The way I do it is. you will need a program like winscp.
1. Login to your site with winscp.
2. On the left side of winscp is the computer you are on and on the right side is your server.
3. Make sure the plugin you downloaded is unzipped and open the folder to where you see another folder. Example c:\download\hint2020\hint.
4. In your server go to the folder ow_plugins and click on it...Then on your side go to the plugin you have downloaded and open the unzipped folser and you will see another folder right click on that folder and then go down to where it say's upload and click on upload. the folder you upload will over write the old folder with the same name.
5. Go to your server with your browser like google chrome or internet explorer and login as admin then go to manage plugins and when you do it will ask if you want to update the plugin you just uploaded click yes.
Your are done upgrading the plugin.
P.S. yoou can also upload new plugins the same way.