Want to Increasing of RAM for HP Probook 4540s ( motherboard HP 17F6)

[RUN05]

I wanted to increase the RAM on my laptop, where Already are 4gb RAM installed in slot 1.
DIMM
Memory type DDR3L
Module format SO-DIMM
Module Manufacturer(ID) Samsung
Size 4096 MBytes
Max bandwidth PC3-12800 (800 MHz)
Manufacturing date Week 04/Year 13
Number of banks 8
Nominal Voltage 1.35 Volts
EPP no
XMP no
AMP no

Now i want to add another 8gb ram in slot 2. 
Question 1. Is it possible to use this 4 gb  previous ram & a new 8gb ram at once? (is it possible to use this kind of combination of 4+8= 12 gb ram?)

Question 2. If I don't use the previous ram then what is the maximum capacity of ram i can use per slot in this mother board ?? ( ram  size & bus speed)

My laptop:
HP ProBook 4540s
CPU: Intel(R) Core(TM) i5-3230M CPU @ 2.60GHz
Motherboard: Hewlett-Packard 17F6, KBC Version 58.1F

Display adapter 0
Name AMD Radeon HD 7650M
Board Manufacturer Hewlett-Packard
Memory size 2 GB
PCI device bus 1 (0x1), device 0 (0x0), function 0 (0x0)
Core clock 300.0 MHz
Memory clock 150.0 MHz
Performance Level 1
Core clock 400.0 MHz
Memory clock 900.0 MHz
Performance Level 2
Core clock 500.0 MHz
Memory clock 900.0 MHz

Display adapter 1

Name Intel(R) HD Graphics 4000
Board Manufacturer Hewlett-Packard
PCI device bus 0 (0x0), device 2 (0x2), function 0 (0x0)
Core clock 350.0 MHz

[Paul_Tikkanen]

Hi:

Officially, according to chapter 1 of the service manual, you can only install 2 x 4 GB of memory.

http://h10032.www1.hp.com/ctg/Manual/c03758231

However, you can actually go as high as 2 x 8 GB of memory, but when you do, there is a problem, that can be easily resolved.

See this discussion...

https://h30434.www3.hp.com/t5/Notebook-Hardware-and-Upgrade-Questions/Performance-degrades-in-Proboo...