Original sentence: This means that customers have unlimited usage and need pay no extra charges related to the amount of data  downloaded, however between 4pm and midnight speeds will be reduced once a certain amount of data (350MB for the 2Mb package, 750MB for the 4Mb package and 3GB for the 10/20Mb package)has been downloaded.Virgin Broadband plans to increase the 10 Mbit/s service  to 20 Mbit/s as of 2007-05-01  At the same time they have also introduced traffic management to prevent a small percentage of users with very large download volumes from adversely affecting overall performance of their network
Edited sentence: This means that customers have unlimited usage and need pay no extra charges related to the amount of data downloaded, however between 4pm and midnight speeds will be reduced once a comparatively small amount of data (350MB for the 2Mb package, 750MB for the 4Mb package and 3GB for the 10/20Mb package)has been downloaded.Virgin Broadband plans to increase the 10 Mbit/s service  to 20 Mbit/s as of 2007-05-01  At the same time they have also introduced traffic management which will impact many customers downloading even a comparatively small volume of data