Computer cpu swap. 2.3 to 2.8 ghz. do I have to update bios?

I have a compaq presario 2500 laptop. came with 2.3 ghz. processor and 512 mb of ram. I came across a dell laptop parts donor. it had 2.8 ghz processor and 1gb of ram. swapped the parts. ram first. works great. then decided to go ahead and try the cpu swap. fits perfect. the computer still works but is slower. in my computer properties it recognizes the 2.8 ghz processor but think it is running at 908 mhz. the number below the processor. I have been told that I need to update the bios if so how. I have also read about changing the voltage to the cpu in the bios. but what would I change it to and how much is to much?Computer cpu swap. 2.3 to 2.8 ghz. do I have to update bios?I would put your orginal cpu back in. Running the replacement at 908mhz indicates the chip has suffered deterioration. Althought the 2.8ghz is bigger in number it sounds like your cpu didn't have any deterioration.