How do I block a contact on the Z10?

I want to block a contact on my z10 device.. but I'm unable to do so.. so please help with with the same...

I am not sure that it is possible with an official OS without using a third-party app like Power Tools Power Tools updated with new features and support for the Blackberry Passport | CrackBerry.com .

The new OS 10.3 will allow contact blocking.