1. search online (dell support) for the service manual
https://usermanual.wiki/Dell/DellInspiron151564ServiceManual111750.1468768577/view
- read through everything
- get your tools ready and heat sink compound (PREFERED ARCTIC SILVER), Alcohol.
- follow through all the instruction on the Service Manual
- you have followed the instruction to remove everything except the LCD
YOU GOAL
A. REACH THE CPU ASSEMBLY
B. REMOVE THE DUST STUCK IN THE COOLING FIN {BETWEEN THE FAN OUTLET AND THE FAN ASSEMBLY}
C. REMOVE THE OLD HEAT SINK COMPOUND and use sand paper and clean the copper side of the heatsink
D. RE APPLY THE HEATSINK COMPOUND WITH THE NEW ONE. (2 MM THIN).
Order the memory for the laptop from DELL or check with Kingston.com
for the compatible type of memory.
DON'T BUY FROM THE COMPUTER SHOP AT ALL
they will give some gibberish random useless memory i.e. KVR ram.
This type of memory will work for first few weeks after that it will slow down the system and worse crash your windows operating system.
Comparing RAM Price you are better off with Kingston than DELL HELL.
Because DELL is always over price and over kill.