If you ever wanted or needed to change the password of an ethereum account here is how do to it, first of all an ethereum wallet has no password itself, each account address has its own password which you can use to unlock it and make transactions. this accounts are stored by geth in files on a special folder depending on your OS which are:

Linux: ~/.ethereum/keystore
Mac: ~/Library/Ethereum/keystore
Windows: %APPDATA%/Ethereum/keystore

where ~ is your home folder

remember its a good practice to backup your files, when changing passwords you may only want to keep copies of the recent files, the ones with the new password.

In order to be able to change your account passwords you will use a working geth executable (ethereum command line client) on your OS.

Windows and Linux

If you have a working geth executable you can skip this part and go to listing accounts , If you do not have it installed but have a working copy of the Ethereum wallet or Mist, you have a working geth executable under a folder inside the Wallet/Mist application folder, look for it inside the folder you extracted the app after you downloaded it in the following subfolder: /resources/node/geth/

Once you find the folder rigth click on it and click "open command window here" on windows or its "open terminal here" equivalent on linux. on this window you will write the geth commands.

Mac

On Mac you will need to have a working geth executable installed, if you only have the wallet/mist on Mac the way the wallet/mist application is packaged on Mac makes it harder to use the geth executable from inside the .app file of the application. so you will have to install geth following the instructions.

Checking geth

You can write this on the terminal window to check the geth command is working and get the version, if you are using the geth from wallet/mist you have to change geth to ./geth so it works.

Linux / Mac: geth version (or write ./geth if using geth from wallet/mist)

Windows: geth version

Listing accounts:

Write this to list the existing accounts on your keystore folder

Linux / Mac: geth account (or write ./geth if using geth from wallet/mist)

Windows: geth account

After that you will get a list with your accounts and a index number wich is associated with it like this:

Account #0: {someaddress} /home/user/.ethereum/keystore/UTC--2016-01-30T20-34-04.552637823Z--someaddress

Account #1: {someaddress} /home/user/.ethereum/keystore/UTC--2016-01-30T20-34-04.552637823Z--someaddress

Account #2: {someaddress} /home/user/.ethereum/keystore/UTC--2016-01-30T20-34-04.552637823Z--someaddress

Changing the password:

next you choose which account you want to change the password, lets say you want to change the password of account #0

then you write this:

Linux / Mac: geth account update 0 (or write ./geth if using geth from wallet/mist)

Windows: geth account update 0

where 0 is the index of the account you want to change the password.

After that you will need to input the actual password of the account, and give the new password 2 times to confirm as shown here:

Unlocking account 0 | Attempt 1/3

Passphrase:

I0719 19:48:53.655255 cmd/geth/accountcmd.go:189] Unlocked account someAddress

Please give a new password. Do not forget this password.

Passphrase:

Repeat passphrase:

And that's it you now have changed the password for that account!

If someone knows a way to run the geth command from inside the wallet/mist .app file on Mac please post it on the comments below, It would help people that does not want to install geth as an executable but have the wallet/mist app already installed.

tokyo3