If you choose to upgrade automatically you will be taken to a page that asks for your FTP information. Your browser will probably save your hostname and username so you will probably only need to retype your password. Hitting the "Proceed" button will deactivate the plugin, download the new version, unzip and install it, and then reactivate it.
If you are unfamiliar with how to install addons for yourself, this is a handy way to keep your site up to date without having to contact your programmer. Most of the time this will work fine with no bumps. This is however an automated process and can't think like a human, so be sure that your site is backed up on a regular basis incase something goes wrong. Also keep in mind that this will replace all of the files in the plugin, so if you have any customization that you don't want overwritten, you will want to manually update the plugin.
