Changing memory speed in bios

Welcome to Tom's hardware,and hello there

Where did you see these MHz specifications about your ram?

i think that the 400MHz ram on your pc is presently running at a lower rate of 333MHz.Since the ram module is a double data rate,(ie.at rising and falling edges of each clock is used for data transfer) the actual clock should be 167MHz and the effective rate or the rated speed becomes twice your 167MHz which is read as 333MHz.

I think you might have read the actual clock and the rated or effective clock at different places which made you think that your ram is running slower at 167MHz.
Try CPU-Z which is a good software to determine various properties of your ram.Try and see what speeds are supported under CPU-Z and your present clock frequency of the ram.