So, I have this windows 8 with 8 GB memory, windows recognize the memory but when I open task bar, I see 4.5 GB hardware reserved memory

AMD A10-4600M with AMD Radeon 7660G + 7600M with 4GB x 2 memory

There is no way to change the bios, because its totally locked
Anyway the issue is not on software, but more to hardware issue

At worse, this can be indicate that your memory module is faulty

BUT before you decide to buy a new memory, try to swap it first,

on my case it works!, now the hardware reserved memory only 549MB 🙂