Will my older pc be able to run windows 10 or at least Windows 7?

It isn't that old, about 2 to 3 years, 4 max, it has Windows 7, it's an all in one Acer touchscreen pc with 1TB Hard Drive and 4GB RAM, i'm not sure of the processor ect cause i'm not home right now so i can't check, any ideas at least? Will it also slow me down in any way? I intend on upgrading the ram to run minecraft a little better, but i don't want a new OS to ruin that.

Added (1). I apologise, I meant Will my older pc be able to run windows 10 or at least Windows 8.1?

The system requirements are almost exactly the same for Windows 7, 8, and 10, so if it runs Windows 7 well, it will run Windows 10 well.

The system requirements for the Windows 10 test version are on this page:
http://windows.microsoft.com/...q#faq=tab0

I honestly don't see any reason to upgrade to 8.1 unless you just want better touch screen support. It's basically Windows 7 with a new touch screen optimized start menu and slightly faster boot times…

Yes all of the above

Yes and no depends on your tech specs CPU and GPU Windows 10 you might need new computer or upgrade your current one for best performance.