To expand AS70 series memory to 16 GB, please follow the instructions in the video to upgrade the internal memory, making sure to install 8GB memory to both internal and external slots.
Other compatible memory which you can buy locally: http://www.asustor.com/service/memory?id=memory
Description: 2GB DDR3-1600 204Pin SO-DIMM RAM Module
Dimension: 67x30x10 (mm)
Applied Model: AS7004T / AS7008T / AS7010T