Windows 10 disk image

Microsoft has released a Windows 10 tool to download the required files and make an install DVD disk, USB or ISO image:
http://www.microsoft.com/en-us/software-download/windows10ISO

If you have multiple PC's that your upgrading and you don’t want to download 3+GB of data per PC this is the way to go. Also doing this at a time that you specify may be better than risking your PC's auto updating at the most inopportune moment.

The install media also gives you the ability to erase your PC and do a fresh install (after backing up your data) just bear in mind that the mechanics of how licencing and product keys work in terms of your free entitlement is still unknown present.

My initial "don’t upgrade yet" recommendation still stands unless you are a "tech enthusiast" and either way I highly recommend you take a full "system" backup first see here for more detail.