2x DDR3 slots, supporting up to 16GB total (DDR3-1600MHz) .
Since you found this manual, you likely want to upgrade this old system. ms7869 ver 10 motherboard manual 2021
Micro-ATX (24.4 cm x 20.6 cm) Socket: LGA 1150 Chipset: Intel H81 Express 2x DDR3 slots, supporting up to 16GB total (DDR3-1600MHz)