depreciation calculation for previous year

hi

iam facing a problem that the depreciation for the particular asset class with particular assets has to be increased . for example

i purchased the asset in 2005. i depreciated the asset at the rate of 4.5%. now it has to be increased to 10% not only for this year , but also for the past 2 years with out getting effected to this previous year posting.

for some assets it has to be reduced.

ex asset purchased at 2005 . they charged dep at 15%. but it has to be charged only at 10 % for the past years and also the current year.

how can i do the following things.

it has to be done immediately pls help me out.

balaji.p.r.