Upgrade android version 4.1 Jellybean to Lollipop 5

Ok, so here's the thing (and bear in mind I'm a complete technical Luddite)

I have a tablet....Fujitsu M532 :rolleyes:..which I bought in Lidl a couple of years ago.
It's grand for what it does, but it's started to play-up, so I thought I'd, well, "do a job on it".
I've rooted it - successfully (whatever that means) and I'm now looking to update the android OS from 4.1.1 to 5.0....or something more reliable.

I've been searching the web for a way to do it, but all I seem to come across are links to websites that want me to sign up to a premium rate text messaging service before allowing me to download the software (they can FRO)

I think part of the problem is that the tablet manufacturer isn't all that well known, so getting upgrade stuff is nearly impossible.
There's nothing on the manufacturers website, and as far as i can tell from trawling through the forums, there's no plans to continue support

Anyway...after going round and round in circles, I came across this:

http://androidlp5.com/androidfw_2901.html

.....which would appear to be EXACTLY what I need.

Questions are:
1) reliability/security of the site
2) am i taking my balls in my own hands by downloading the software and installing on my tablet
3) am i better off just handing the tablet over to the chizzler and investing in a new machine

All helpful comments GREATLY appreciated.
Thanks Folks