Firstly, your casing is small, and that would cause some
problems:
From the picture on hp website, it seems like it is a small
system.
And because it is a small system, you might have problem finding
a powerful powersupply that will fit into the box, because in order
to run a graphics card of higher spec, the power requirements will
be higher, and the type of powersupply that can produce those power
are generally bigger in size, and may not fit into your casing.
Also, if the casing is small, you are limited to only low
profile graphics card, and that would mean not being able to fit in
those giant graphics card.