Memory:  2X16 =32 G max. Storage:  one M.2 2230 and one M.2 2280 (the latter is available up to 2T that will fit the system;  the former is smaller and limited to 1T).  
How much RAM does the Dell Inspiron 15 5518 support? And since it has dual SSD slots, how much storage does it supports. It might look like a silly question as I am a Mac user since 9 years.
RAM and Storage Max Capacity