When upgrading from one full version (4.7) to another (4.8) you need to follow the upgrade directions in the upgrades directory.
0) Download and unzip the latest build from the Members Area.
1) Check for new config-inc.php variables, some recent additions are:
$cookie_domain has been added for website cookies. I highly recommend setting this to ".youdomain.com" where yourdomain is the name of your domain. This will enable cookies to be read across your website regardless of the URL (i.e. galley.website.com and forums.website.com). If you are using a forum integration you must have this set in both your forums and photopost.
$vblicense is for VB3 users and is required to encrypt your passwords. Without it you will not be able to login to VB3.
2) Upload all files - except config-inc.php, unless you modified it from the ZIP file - to
your server. You do not need install.php for an upgrade.
3) Depending on which upgrades you need, you should upload all these files to the MAIN PHOTOPOST DIRECTORY (or, for advanced user,
upload only those scripts you need to execute).
4) Run upgrade.php and depending on your version, run any necessary upgrades.
5) When done with upgrades, remove the upgrade*.* files which you uploaded from this directory.
6) You are done!