We typically don't answer direct emails as it doesn't allow a topic to be tracked or others to address it. My email actually deletes anything with a link to a topic as spam, not sure about any of the others.
For updating, you just download the theme files from your downloads on themeforest. The main package will have the theme docs, license and other files inside of it as well as the actual sentence.zip file that can be uploaded through the wordpress admin as the actual theme.
You can just upload that zip using the wordpress admin unless your setup doesn't allow writing over the files. In that case, you'll need to upload the theme files via FTP.
If you've made any changes to the actual theme files, make a backup of all those files locally. After you update, you can check the version.txt file that was in the main package you downloaded from themeforest and see if any of your modified files were changed in the updates. If so, you'll need to re-add those changes individual instead of just writing over the entire file.
Then update Wordpress to 3.5 as well as any plugins you have running since some things were changed in 3.5 and many plugins needed updating.