Just Do It
How can I transfer data from existing memory card to the new one without losing any data ?
thats easy...first copy your data to a pc.then insert the 16 gb card in your phone and copy the data back.
^^ exactly. unless the 2GB card is partitioned (which is not possible on stock rom), simply copy paste it.
OK, won't I lose the installed apps ?
But what about contacts, sms, etc ? Which software can I use to do this backup ?
you will lose your sms