How to change KB into nibbles?

You need to learn what the words mean. The K stands for kilo, which is Latin for 1,000, but in computers 1,024 is also called a K. So your question is unclear.

The B stands for byte, which is eight bits. Nibble is a whimsical term for half a byte, four bits. It is only used to translate a byte into a hexadecimal number.