Remove nine screws securing the bottom case, pry up and remove it.
Under the bottom case, you can access the SSD, wireless card, battery, speakers, heat sink and cooling fan.
Dell Inspiron 11 3158 comes with a 2.5″ Samsung 128GB CM871 SSD, we using AS SSD software test the SSD, the maximum read speed of 463MB/S, the maximum write speed of 125MB / S, 4K access, random access time score all belong to the mainstream level.
If necessary, you can replace it by Samsung high-end 2.5″ SSD.
Inspiron 11 3158 hardware upgrade space is not really rich, you can only replace SSD, RAM, wireless card, you can upgrade the RAM to 8GB (not sure its support 16GB, you can contact dell to confirm it).
The Dell Inspiron 11 3158 built-in a 43Wh lithium battery, using the built-in player continuous playback 1080P video for 2 hours (80% screen brightness, 15% of the sound, connect to wireless network), for a total power consumption of 25%, based on projections, the life time approximately of 8 hours