As you may already know there 2 way to manage user accounts on Office 365:
- From the cloud, using Office 365 administration portal (https://portal.microsoftonline.com) or using PowerShell
- From your on premises – so your own AD, using the Active Directory Synchronization tool, called DirSync
The latest release of DirSync is now including a long waited feature: password synchronization
This was a long wait feature as until now, there was no way to synchronize your on premise password except by implementing ADFS which is NOT password synchronization but redirecting authentication processes to your on premise AD; this means in case of your ADFS is not available, there is no way to access your Office 365 data.
So, the new DirSync release now offers to synchronize your AD password with your Office 365 account.
Go to http://go.microsoft.com/fwlink/?LinkID=278924 to download the latest release (only available in 64 bits version).
The install process is mainly the same than previous version of DirSync – if you already had DirSync installed you have to uninstall it before; don’t worry, you will not loose your existing account and the next sync will not be a full one 
. You can check this post for the installation process http://blog.hametbenoit.info/2011/05/26/office-365-install-and-configure-directory-synchronization-dirsync/
You may have a .Net Framework error related to security permission; just right click on the installation file and choose Run as administrator
Once installed, during the configuration process you will have a new step called Password Synchronization; if you want to enable it, just check the box
To know more about this new feature, go to http://technet.microsoft.com/en-us/library/dn246918.aspx