JavaCard OS

I have installed my applet into the smart card. My question is how to prevent others from changing the content of my card.
I mean, I want to "lock" my card. So that nobody can change or delete my applet.

Here are two methods for you to "lock" your card.

1. Change the authentication keys to achieve your goal and be sure to save the new key in secret.

2. Set your own PIN.

How to set my own PIN??.. Please elaborate