Paint Tool SAI non-trial version for free?

I have a lenovo thinkpad and I was looking for Paint Tool SAI for free (and not the trial version) and if you could provide a link that's be great, but Please give me a reliable link 'cus I'm pretty sure I got a virus last time I tried. But anyway, I really appreciate your help thanks!

Why is my laptop gradually lagging/slowing down?

Why is my laptop gradually lagging/slowing down? - 1

Added (1). I have a decent knowledge when it comes to computers and electronics, I know most of the reasons as to why laptops/PCs degrade as time comes. This time, however, I have had a more powerful and reliable laptop.

I have the Lenovo P500 laptop
Hard Drive: 500 GB
RAM: 6 GB
Processor: Intel Core i5 3210M

OS: WIndows 7 Ultimate (Used to run Windows 8)
I also have a decent Graphics card that can handle big video games.

Added (2). This laptop runs amazing, used to run even better. It would startup in less than one minute and do tasks that would take upto 2 minutes on my old Toshiba.

However, its been over a year that I've had it and I'm starting to realize definite signs of lag and slow commands. There's no malware, no viruses and I have plenty of storage left.

I do have some pretty huge games and programs installed:
GTA 5
PES 15
NFS Hot Pursuit
Rome 2 Total War
Skyrim… At least up to 12 video games

Added (3). Ok so with that said, I was wondering. Is it these programs that are causing the lag on the laptop,
is it time itself that is making this laptop old, and unable to keep up
or is there something that I may have missed.

Can i upgrade my laptop cpu and gpu?

My lenovo b50-70 has i3 4030u and hd4400
and another variant of the same model has i5 4200u and gt820m/r5 m230
so can i upgrade to those specs by replacing these components on the motherboard from a shop?
this would give a big boost in performance

Does This laptop have a disc drive?

Me an my sister are getting a laptop to play sims 4 but does this £200 Lenovo 11.6 S21e Intel Pentium 2GB 32GB eMMC Silver Ultra Portable Laptop have a disc drive!

Error when installing windows 10?

Error when installing windows 10?

Added (1). I got windows 10 education from dreamspark through my school and put it onto a bootable usb (I've done this before with windows 8). I run the setup in the flash drive and it starts to install but after restarting it goes to a black screen with no cursor. I tried shutting it down manually and it comes back on in windows 7 saying error, couldnt install windows 10. Am I doing something wrong or does someone know how to fix this? I have a lenovo e455 thinkpad with windows 7 if that helps

Can I play these games on this laptop?

Laptop: Lenovo ideapad 8gb ram, 1tb HDD, Intel Pentium n3540 quad core processor, shared graphics card ( I don't know what that is )
I would like to play:
Minecraft with no lag
Skyrim
Fallout 3
Fallout new Vegas
Also I was wondering if it could play new games like the witcher 3 even if I had to use low graphics.
Thanks and does the ram matter that much because I can get a 4gb model for cheaper.