Need to change beginning balance on one account 'Account #000-1009-00" and I need to “unreconcile” so it has have the correct beginning balance as of 8/31/15

All,

I need to change beginning balance on one account. Account #000-1009-000 and I also need  to “unreconcile” so it has have the correct beginning balance as of 8/31/15.

Any suggestions on how I can do this?

Regards,

Deborah