A red padlock is made by creating an accountant export.
To remove one:

Be in either Money In or Money Out.
Go to [File] in the top left
Select [Accountant Export] and [Unlock Months]
Tick the months you want unlocked
Then click [Unlock] in the bottom right.

A yellow padlock is made by reconciling your month.
To remove one:
Go to the Bank Reconciliation for that month
Click [Unlock] in the bottom right.

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