If its any help to you, I upgraded my 2011 Dell XPS15 (i5) this Christmas to celebrate BT finally delivering Infinity to our village.
I put in a Samsung 850 EVO 500GB SSD (circa £110 from Amazon) and cloned the existing HDD using Samsung's supplied utility, (needed a usb to sata cable for this). Also bought a genuine Dell battery for £40 from Ebay.
Was a bit concerned about Win 10, as mine was an upgrade from original Win 7 and have seen mutterings that a fresh Win 10 system would be more stable and I was getting a BSOD about once a month
It seems that the MS offer to upgrade Win 7 to Win 10 expired some time ago and you cannot do the 7 to 10 upgrade now. I log on to Windows with my Microsoft account, so knew my license was registered and activated, therefore I purchased a Win 10 pro oem license key from Amazon (around £10, now up for £4.49). This enables you to download a fresh Win 10 pro from Microsoft and install it using the purchased key.
Anyway, it all worked and the laptop now flies.
Suspect its on borrowed time though, as I found out Intel now state they don't support my machine's on-chip graphics driver for Win 10. But the driver version on my machine has a higher number than the last one listed on the Intel website, so maybe MS persuaded them to produce a compatible version when Win 10 was first released. Certainly I have never applied an Intel driver update, so can only assume MS Windows Update has updated it.
If it lasts a couple of years I will be happy; for £160, the machine is noticeably faster, more stable and has had its replacement delayed for a useful period.
PS the old HDD can be used for backup/extra usb connected storage.