If there is an update available, you can check, download and install from the Software Updates menu, which should be somewhere in Settings > About.
If there isn't, you have to either wait for HP to produce one or root and install a custom ROM, if such a thing exists for your tablet (which depends on someone writing one). Rooting also invalidates the warranty on the tablet.
Android software always has to be built for the particular device. There is no generic Android 4.3 which can be installed on any device. Hence, unless custom software exists for this tablet, you cannot update until HP release an update for it.