You can configure synchronization options for any of your apps. You can also configure what kinds of data you synchronize for each account. Some apps, such as Gmail and Calendar, have separate synchronization settings that provide more fine-grained control. In such cases, the settings you select at the account level are still valid.
For some accounts, syncing is two-directional; changes that you make to the information on your device are made to the copy of that information on the web. Your Google Account works this way. Other accounts support only one-way sync: the information on your mobile device is read-only.
To view the Accounts & sync settings screen described here:
Some apps also have their own settings related to syncing. For example, to control message syncing in the Gmail app, touch Menu icon > Label settings > Sync messages.
Configure general sync settings
If you turn off Auto-sync, you need to sync manually to collect messages, email, and other recent information, and won't receive notifications when updates occur.
For example, when this option is checked, changes that you make in your People app are automatically made to your Google contacts on the web.
If this option is not checked, you may be able to use an application's tools to sync data manually. You can also sync manually to collect messages, email, and other recent information. Leaving Auto-sync off can help extend your battery life, but will prevent your from receiving notifications when updates occur.
Sync information manually
Change an account's sync settings
Unchecking an option does not remove the information from your device; it simply stops it from being kept in sync with the version on the web.