Help! RAM Upgrade Issue

My laptop is old now, So i don't hope for an answer to this. This laptop was given to me by my cousin and it has 4GB PC3-12800S of RAM installed. Back to the question, I checked online for the ''MAXIMUM RAM does the laptop can handle and found out that it can upgrade up to 16GB RAM DD3 1333MHZ, And now I purchased extact PC3-12800S 8GB of RAM installing it to the laptop hoping to have 12GB RAM installed booted up and checked the "System Information" and was working fine next is checking the "Task Manager" and seeing it consume half of the memory in the "Process" Tab (it was 54% of memory used)'' and i was wondering "why i have 54% used memory i just opened the Task Manager" and i switched to check Performance Tab hoping what's wrong with the RAM installed and seeing the RAM Usage was 1.9GB/3.5GB and the newly installed RAM is not used seeing the "Hardware Reserved" was 8.5GB. I searched every way possible to solve the problem and nothing works. What seems to be the problem?

Laptop specifications: AMD A8-3520M APU with Integrated Graphics AMD Radeon HD 6620G Windows 10 64bit