Make sure windows 7 or 8 is on your hard drive ready to be upgraded.
Either will probably work:
1) Create a new administrator user in windows
2) Log in as that user
3) Run install DVD.
Corrupted users accounts are causing Win10 upgrades to fail.
The other alternative is to run the install DVD as the current user, and make sure you select the clean install option wiping all apps etc.
If you've just done a fresh Win 7 or 8 OS install you can probably just run it straight away without above work arounds.
In all cases you will get a license.
Do not boot off the CD when starting your PC, run it from windows.
If you want an entirely clean install (because a clean install isn't really a clean install!!l), boot off the DVD when starting your PC, and install windows again after formatting the partition. However DO NOT do this until you have installed Windows 10 at least once via the methods listed above.
Always backup first with something like acronis if you have data !!!
Cheers.