Hello @Sahil_Ahlawat
The specs show your model came with only a 1 TB HDD.
You can add an M.2 SSD, it will be compatible with either an NMVe or Sata M.2 drive.
And you can also swap the HDD with a 2.5 inch Sata SSD.
There is no capacity limit for either one.
If you are going to add an M.2 drive and put the OS on it, keep the Sata SSD/HDD disconnected during the process to make things easier.
The memory can be upgraded to 16GB total according to the manual.
If you are going to add the existing 8GB stick, you need to match the timings of it with the new one.
Use a tool like GPUz to find the existings timings, and buy a new stick with the same.
Here is the manual that explains how to access the hardware...
http://h10032.www1.hp.com/ctg/Manual/c05985643
Let me know if I can help further.