Hello, I see that you are interested in knowing if this Pavilion will be able to upgrade its memory to 16GB. The answer is Yes! The pavilion 21.5 supports 1 GB, 2 GB, 4GB and 8 GB DDR3 SO-DIMMs. supports up to 4 GB on 32-bit systems and supports up to 16 GB (unbuffered) on 64-bit computers.
Hopefully that helps you out and thanks again for choosing HP.