How do I undo someone's error and put in the correct data for myself?

There are two examples: the first is the disk is automatically populated with The 4400: The Third Season (Disks 1 & 2), however the disk inserted is only Disk 1. 
IMG="http://img341.imageshack.us/img341/5701/disk1.jpg

The second one is when adding the other disks from this season, it shows a classification of 12, but it is a 15.  When I click on Certificate it only gives 12, 16 and Adult.  Above it says Rating System Kijwijzer which I assume is where the problem is, but doesn't give the BBFC system as an option.

Quoting SanderDolphin:

Quote:
How do I undo someone's error and put in the correct data for myself?

There are two examples: the first is the disk is automatically populated with The 4400: The Third Season (Disks 1 & 2), however the disk inserted is only Disk 1. 
IMG="http://img341.imageshack.us/img341/5701/disk1.jpg

The second one is when adding the other disks from this season, it shows a classification of 12, but it is a 15.  When I click on Certificate it only gives 12, 16 and Adult.  Above it says Rating System Kijwijzer which I assume is where the problem is, but doesn't give the BBFC system as an option.

Add the disc.

Then go to DVD->Change Locality and check which Locality it is. Given your statement I assume it's The Netherlands. Change it to United Kingdom (I assume that's where you bought it [hence the BBFC rating]).

Then you can do the appropriate changes and contribute it according to the contribution rules

PS: The other data is not an error, it's just another locality (country) for the same disc.