Provided you have an active licence, your plugin can be updated from within your WordPress admin.
Just go to the Plugins page in your admin and checking whether an update is available next to your plugin’s name.
Just click the ‘update now’ link to update to the latest version.
Note that you will need to have your licence key entered to be able to receive updates.
I don’t see an update available
If you don’t see an update available on the Plugins page but you are expecting one, you can go to Dashboard > Updates and reload the page a couple of times. This will trigger WordPress to go looking for updates.
Are you running iThemes?
The iThemes Security plugin has a setting which may affect updates. To fix this, go to Security> Settings> System Tweaks and disable the Filter Suspicious Query Strings in the URL setting.
I still don’t see an update
If you’re still not seeing an update, and you have your licence key entered, then go to your Account page and download the latest version. You can upload this via FTP. You won’t lose any data this way; though it’s always wise to take a back-up before making changes like this.