How to delete data off a real dvd?

Hi I just joined. My friend bought a dvd from a different region and I used clone dvd and any dvd to fix it but when i want to copy it to another dvd its only 71 percent quality (because it automaticaly compresses itself so it can fit the dvd) so im asking if there is a way to delete the data off the original dvd and copy the data onto the original dvd so it can be 100 persent quality.

thank you for your help:)

Hi and welcome vinay666:

You can either use a DL disk (only use Verbatim) and it will not be compressed or you can copy the original to 2 SL disks.

Is the 71% reduction the result of “cloning” the entire disk or is it “copy DVD title”?

If you live in an area where Newegg ships, I just posted the following.

http://club.cdfreaks.com/f58/20-pack-verbatim-8-5gb-dl-dual-layer-disc-media-25-99-free-shipping-no-rebates-251325/

Or else you can get a program that will copy movie only

thanks guys i found a 8.5gb dl dvd+r ten pack at the electronic shop near my house:P so thank you jeff!