Why when I set a shader, the shader make some errors like I can't see some titles, I can't see names and it often make my computer slow, what to to?

Turn shaders off. Your computer JUST meets the requirements, but doesn't handle it well.

What are the requirements? I think my computer has all.

Tweak the shaders a bit, but before doing that update your drivers.
then when in tb, try playing with the settings. DISABLE raytracing since your computer cannot handle much.

It's recommended to have a 512MB GPU With a 3.0 Pixel shader.

ok, I'll try

And where to check the GPU?

How to upgrade it?

Buy a new one.

You cannot upgrade a GPU. You can only get new drivers to boost performance a little bit.
I used to have 25 FPS on Burnout Paradise, It looked weird to me because I have SLi, I updated my drivers and BOOM 40FPS!

If you are a Gamer, I suggest you Nvidia 450GTS. A very nice card for gamers.