Here's the maintenance and service guide, taken from this support webpage for the laptop.
It shows that there is only 1 ram slot on the motherboard and that the maximum ram module available is 8GB - PC3L (DDR3L), 12800, 1600-MHz SODIMM ram. You will have to remove the systemboard to get to the ram slot as it is on the underside of the board (see p.76 of the guide for the procedure)
According to the parts list for your model the motherboard is part #788287-501. so it has an N3540 CPU which has integrated graphics and it is hard mounted on the systemboard. There is no separate discrete GPU
To improve performance you should be able to upgrade the sata HDD up to a 4TB 2.5" sata SSD (if you need this much storage) without too much trouble. You won't even need a spacer under the SSD to ensure the SSD lines up with the connector as the parts list specs show that it is a 7.0mm HDD in the laptop and most SSD are also 7.0mm in height whereas some other laptops have a 16.5mm sata HDD, so a 9.5mm spacer is required to be placed under the SSD to raise it to the requisite height.