basically i let my brother use my laptop and he found some of my chat logs which had a password but he somehow knew my password. He has taken them off my computer and put it on his computer. I want to change the password so that he can't go in on them anymore rather than me deleting them. Can anyone help me? i've already tried to have a look and see ho it is possible to change the password but ive had no luck

Yes, you can re-encrypted them with another key.

Open the plus settings windows by typing '/prefs' in a conversation window. (don't worry, your contact wont know.)

Then go to the Conversations tab, then logs encryption on the left.

You should see 'Re-Encryption', from there you can change the password of the files and above that you can choose a new password for new files that are created.

Good Luck.

On top of that, I'd add more security to the computer itself, i.e. a password for Windows, so he can't get on the PC in the first place. Get the screensaver to come on after 5mins or so and re-ask for the password. Also lock your PC (shortcut: Windows key + L) when ever you leave it.