Thank for the replies.
After a bit more reading I've decided to go down the fresh install route, but I'm a bit confused by licencing;
I've got two M2 bays, one currently occupied by the main drive & the other empty. The plan was to backup as required, install a new SDD into bay 2 & then install Win 10 onto this, retaining the original SDD via dual boot for a while before repurposing it. Win 7 was OEM installed via Win 10 downgrade rights, so I have Win 10 recovery media which I can use to install Win 10.
I'm no doubt overthinking this, but as Win 7 & Win 10 will be running on the same licence will there be any issue with doing as I plan - I'm thinking that 2 almost concurrent copies of Windows, running on the same licence on the same PC may be an issue?
Thanks.