Hey, For doing so you will require a Migration certificate that you can easily access from the JKBOSE official website. You can apply in the CBSE board school, they ask you for the documents like Migration certificate and Transfer certificate and some other documents that you may ask from the school authorities in which you are seeking admission.

Collect all the documents and complete the process as you will be asked by the school. 

Hope this helps.

For any further details please ask in comments.