Upgrading Plugins

We recently updated our blog and there have been an assortment of issues. One of the issues relates to the plugins. We de-activated all of them before upgrading and they are all there but some have new updates. I click the upgrade button below the plugin and the install fails every time for every plugin.

If I am going to download the newest version and then install it the normal way, is it best to just drop it in the plugins folder on dreamweaver and let it overwrite? Is there a better way to do the plugin upgrades? Do I want to delete the old plugins before putting the newer versions in? For some reason, the upgrades won’t overwrite. Help is appreciated.