Assuming you are already logged in with a current password, click on User CP in the forum navigation, select Edit Email & Password from the left side navigation.
You will see a page that looks like this.
Enter your current password to continue.
Select a new password that complies with the rules to the left and then enter it a second time. The red X's must turn to blue checks. If they don't it means you are missing something there. Once this is completed, and the passwords match, you should be able to click to save your changes.
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