There are 2 ways to unlock a month depending on the colour padlock you have.
 

To remove a red padlock:

1.    Select either Money In or Money Out on the left under Cashflow.
2.     Go to File in the top left
3.     Select Accountant Export
4.     Then Unlock Months

5.     Tick the months you would like to unlock

6.     Click the unlock option

To remove a yellow padlock:

1.   Select Bank Reconciliation on the left under the Cashflow section.
2.     Click Unlock in the bottom right.

Note: If both colour padlocks appear for you, you will need to follow the steps to remove the red padlock first then follow the steps for yellow padlock.