If your organization wants to change its accounting method, then you have to file the current version of Form 3115, Application for Change in Accounting Method to request for a change as the change in your accounting method requires IRS approval.
If your organization is under Section 501(c) which comply with the FASB codification 958 (ASC 958), then the organization is not required to file a Form 3115 to change the accounting method.
Any organization that has changed its accounting method irrespective of filing Form 3115 should report any adjustments required by Section 481(a) on Line 20 in Part I of Form 990 EZ.
You can reach out to the IRS in advance and request permission to change your organization's accounting method. Failure to make the request can result in penalties imposed by the IRS. To avoid penalties, make sure you whether or not you must file Form 3115 with the IRS.
Note- You must file the organization's first income tax return before requesting for a change in the accounting method.