If you feel your HTC Surround is completely useless with only 16 GB, and you don’t mind destroying it in the process of upgrading it, Pocketnow have published a step by step video detailing how to get deep inside your device and swapping the memory card.
Now I think 16 GB is quite a bit, but if you have a deep and undeniable yearning for more, see full instructions at Pocketnow here.