In a case, i need to modify the financial statements which is shown after 2016 year-end. There are something wrong and I need to modify it and make it under US GAAP.

1. There are $5000 account reveivable is estimated that can not be collected at the year end.

Original method: Direct write off. Should I modify it to Allowance method because of the GAAP? Please describe the reason and give the adjusting entry. And what effect will it be modified (in financial statement and other aspects to talk)?

2. I find the depreciation has error from 2012 which is the beginning year of depreciation. It should be $2000 each year for depreciation, but from the first year 2012, it was reported as $1500, it continued to be reported until now the 2016 financial statements. How can i modify the error in 2016? Please give the adjusting entry. And what effect will it be modified (in financial statement and other aspects to talk)?

Thank you.