If you wish to change the password you use with Minecraft just follow these simple steps:
1. Visit http://www.minecraft.net/.
2. Next just sign in to your minecraft account, click on Log in link at the top of the web page.
3. Click on the Profile page link on the web page.
4. Now click the link under the section titled Change password.
5. Next enter your current password then enter your new password twice.
6. Press the Change password button, you have now changed your Minecraft password!