Quick credit card question

[DosXX]

I am 22 and only have one credit card I've always paid the balance on each month since I was 18. Its a citi card. If I want to "switch" to another type of citi card, will that close my old account and open a new one (bad). Or will it maintain all the account information and act like there was never any difference (good).

To clarify, I want to keep this credit line open as long as possible, because, from what I understand, that is good for your credit. If I want a new citi card, is it best to "switch" my type of card or to open a whole new account?