To enter the BIOS setup, you must press the key immediately after powering on the computer. Spam the Delete key repeatedly as soon as you see the initial "PEGATRON" splash screen to ensure you don't miss the short window of opportunity.
The H61 chipset was an entry-level platform for Intel's second and third-generation Core processors. The manual listed the supported memory speeds: DDR3 1066 / 1333 MHz . pegatron ipmsb-h61 manual