To my surprise, I am not able to update the gmail account password on my BlackBerry 10 device. Figured that if you choose the default setup where the hub does all the configuration, there won't be any options to edit the server settings or passwords later on. So if you intend to change passwords later, then you should choose the advanced option and choose IMAP account option instead. Key in the details manually, and you will be able to update the password if required. And for the current setup, you will have to delete the account from the device and add it again using the above method.