There are two ways to install a new theme for wordpress:
1- Installing via WordPress admin
- On your wordpress admin, browse for Appearance → Themes and click on Add New button
- On the secondary menu on the top click on Upload press on Choose file button
- On the files you downloaded from themeforest, choose unboutique-theme.zip and press Install Now
- After the thmese is uploaded and installed, all you have to do is to click on Activate button and activate the theme.
2- Installing via FTP
In some cases you might now be able to install the theme via the admin panel, usually because of your hosting plan settings and the file size it allows you to upload via admin panel.
In case you encounter any error using the method above all you need to do is to upload the theme via an FTP client like FileZilla by uploading the unziped folder of the theme right into the themes folder of your wordpress installation.
After successfully uploading and installing the theme you should see the Une Boutique theme on your wordpress theme list.