I will agree with Carl in that this would be best handled by a tax professional.
You certainly can do most of this within TT, but since a significant form will need to be attached to your return, you would need to paper file your return.
In January 2015, the IRS issued two revenue procedures effectively split former Rev. Proc. 2011-14 in two parts; Rev. Proc. 2015-13 contains the general procedures for changing methods of accounting, either with IRS consent or automatically, and Rev. Proc. 2015-14 lists the automatic changes originally contained in the appendix to Rev. Proc. 2011-14.
In Rev. Proc. 2016-29, the IRS issued an updated list of automatic changes to which the automatic change procedures of Rev. Proc. 2015-13 apply. Accordingly, the new revenue procedure amplifies, modifies, and partly supersedes Rev. Proc. 2015-14.
When you file tax returns methods of accounting are adopted. The IRS requires you to continue to follow these methods of accounting unless you seek to make a change. These changes are handled via form 3115. As noted above, some changes are automatically consented by the IRS and others need to be approved (a much longer process). A change to depreciation in general is one of the automatic changes, but you still need to file a form 3115. Typically this form is sent to the IRS National office and also attached to the tax return for the year of change.
The change is handled in the form is what is known as a Section 481(a) adjustment; which can be favorable or unfavorable. Yours of course will be a favorable adjustment.
As you can see, there will be a lot to complete to effect this change. A tax professional can help you complete the form 3115 which will provide you with the Section 481(a) adjustment that will be entered on your tax return. Or alternatively, you can just have them complete your return for the year of change.
*A reminder that posts in a forum such as this do not constitute tax advice.
Also keep in mind the date of replies, as tax law changes.
