How To Change from Jazz Mobile to Warid Mobile

I have an old Jazz mobile phone connection which I want to change but because it is an old number and many of my old contacts have this number I want to keep the number but change service provider. Please give details or instructions on how I can change my number from Jazz to Warid.
Thank you.

There is also an online method but I am not aware of it whether it is useful or not, so I will provide details of the manual way for MNP.
First send 'MNP' to 667
Then forward 667 SMS response to 76321