Hi john,
Our theme is compatible with php7. Which version are you using? Currently the new version is 3.0.3. If you have not used the latest version then download it from account page. Simply deactivate interface pro theme and delete it. Install a new version of it.
please make the backup of interface pro theme which you have currently installed on your dashboard before deleting it.
If you have not customize the code then no you will not loose anything. If you have made code customization in theme then yes your customized code will be lost while updating to new version. You can make a backup from your ftp. Login to ftp/public_html/wp-content/themes/interface-pro