System backup prior to Windows 10

I have now decided after updating my Notebook (thank you all) that I will now update my desktop.
When I backup my system etc. to external hard drive using Macrium can I just back up the C:/ drive?
The D:/ is the recovery drive and although it has 12.9GB it has only a free space of just over 1.88GB and do I really need this as I am making a recovery drive externally?

I'd say backup the entire hard drive, all partitions. That way if anything does go wrong during the upgrade you can get back to where you are now very quickly.

At the very least, you should select the option, "Create an image of the partition(s) required to backup and restore Windows." That'll ensure that, as it says, it'll backup all the partitions needed to make a working backup of Windows.

Thanks Gort, I ended up doing a System Image onto an external hard drive. Downloaded W10 onto the desktop and once again (like the laptop it would not install. Will try again tomorrow.