Credential Storage
If a certificate authority (CA) certificate gets compromised or for some other reason you do not trust it, you can disable or remove it.
1.From a Home screen, touch 
Apps ➔ 
Settings. Under Personal, touch Security.
•Touch Storage type to set a storage type for credential contents.
•Touch Trusted credentials. The trusted credentials screen has two tabs:
–System: Displays CA certificates that are permanently installed in the ROM of your device.
–User: Displays any CA certificates that you installed, for example, in the process of installing a client certificate.
•Touch a CA certificate to examine its details.
–A scrolling screen displays the details.
–Scroll to the bottom of the details screen and touch Turn off to disable a System certificate.
2.Touch OK to return to the certificate list.
3.Touch Install from device storage, then choose a certificate and follow the prompts to install encrypted certificates stored on the USB storage.
You must have installed a memory card (not included) containing encrypted certificates to use this feature.
Note: If you have installed encrypted certificates, touch Clear credentials to erase the credential contents from the device and reset the password.
