So, about 6 months ago I purchased a Lenovo Flex 2 14 from PC World with the KnowHow extended warranty (it wasn't much more expensive).
I now want to install a SSD as the SSHD is on the verge of becoming frustrating to use now. Can I install the SSD myself without voiding the extended warranty?
Read your warranty. It should say what voids it. However usually in most cases it would void the warranty, retailers do that so that you have to buy the SSD from them and have them install you and tax you an additional fee.
Just to say, in case anyone stumbles across this thread, that I fitted the SSD today - Knowhow emailed after I asked and explained that it will not void the warranty - I would just have to put the original HDD back in before any repairs under their warranty.
For anyone wondering though the replacement is comparatively difficult - it's more than a few screws.
I read somewhere that Knowhow fit SSDs for around £25 - and to be honest I'd recommend this after having spent 2 hours on the replacement myself, but yeah it's certainly possible.