Hello @silversong
Upgrading all depends on what you want to play, the game settings (assuming a 1080p monitor at 60Hz) and your "budget".
If all you playing is LoL and similar, then all you need is a GTX 1050.
If you play higher end stuff like AAA games then a GTX 1060 would be in order.
More memory? If your system is needing the ram while gaming then yes it will help.
Tests from a lot a reviewer have shown a significant difference in using 16 over 8. If its available, your system will use it.
You want to match the timings of the existing stick of ram, when installing a second stick.
Use a utility like Speccy or CPUZ to see what you have currently.
Adding an SSD to run Windows from will make the system feel a lot faster also with fast boot times. The games wont play better, but installed to SSD they will load a lot faster. It has one M.2 NVMe slot.
Let me know if you have other questions.