You can't just make changes to the depreciation. You'll need to file Form 3115 to correct the past errors. Depreciation recapture is not irrelevant. Even if you convert it to personal use and exclude the gain, you still have to recapture the depreciation.
One solution is to elect an accounting method change and file a Form 3115 in the current year and take the prior depreciation as a section 481(a) adjustment. [land value is separated, land is not depreciated]
Below are the IRS links related to the change in accounting method. TurboTax does not have that form.
May be these will help
Form 3115, Application for Change in Accounting Method
Change-in-Accounting-Method
Instructions for Form 3115 (03/2012)
Instructions
Form 3115,
Form 3115
