how do I delete an itunes account / apple ID?

Hello,

When I first created an itunes account I used the e mail address from my ISP.

I now want all of my dealings on itunes and these pages etc to be done under my .mac / mobile me details.

How do I delete my apple ID referring to my isp e mail address.

I have changed my e mail address on my info for the discussions section, therefore I presume my macjock name will continue using my .mac login?

thanks