shaun88 :
my PC has downloaded windows 10 but before I install it I would like to know where windows 10 has downloaded to so I can keep a copy for future, incase I need to reinstall it etc
That's not how it works.
Use the link SR-71 Blackbird gave you and install media creation tool, either 32 or 64bit depending what you have.
I've used this to fresh install after an upgrade.
Once you install the media creation tool, it will ask you how you want Win10 bootable on either USB or DVD (which will require burning software to burn) and which version of Win10 to download, there will be only a few selections so make sure you choose the version you upgraded to..Or there will be problems, its simple.
USB is easier, if your Bios allows USB bootup it should be all go.
Win10 will download and the media creation tool will setup the USB for you if you chose that option, just make sure you have the USB plugged, and preferably 4GB minimum for 64Bit version. Some sites say 8GB and have noidea where they got that information. I downloaded 64Bit Win10 Pro and it wanted something like 3.10GB.