Change the depreciation key

Hi,

I have a asset where the depreciation has been too low.

What we need to do now is:

Post an additional amount to the depreciation accumulated so far (actually for 2007, but probably, now is too late, anyway, it is maybe good even when we do it in 2008)

Change the depreciation key, so that we are more accurate this year (it should go from 4,4986 to 4,8688)

Can you please advise on what is needed here and how to do it ?

Thanks,

Sridhar