Generally, to get into BIOS on any HP it's F10. So either keep tapping F10 when you turn it on, or keep tapping ESC until the blue menu comes up and then tap F10 once.
Even once you're in there though, there more than likely won't be anywhere for you to 'tweak' the RAM speed. Genuine HP mainboards / BIOS' don't allow for overclocking RAM or CPU (unless it's a HP gaming PC such as an Omen, perhaps)