Karadjgne :
What Windows is on your laptop? If it's XP, Vista, Win7, 8, 8.1 or 10 x86 (32bit) 8Gb ram will be no good as 32bit OS can only use 4Gb. You'd need a x64 (64bit) Windows to use the full 8Gb.
1) True... it's almost certainly 64-bit Windows (likely W10).
You can check by:
a) right-click Start then "System"
b) under "System Type" it should start "64-bit"
2) just FYI, but it is technically "8GB" not 8Gb (the latter means eight giga-bit not eight giga-byte).
3) *to be absolutely clear, you can use up to an 8GB stick and it absolutely MUST be compatible in every way as I mention before.
If you got ECC instead of non-ECC for example it would not work. No such thing as a bigger stick or higher capacity than 8GB (which is pretty good actually).
If things are sluggish still then an SSD may help. Depends what you are doing... for processing (converting video, games etc) most of the time that's simply the CPU or GPU so nothing you can do... system memory simply buffers data that would normally take too long to load from the OS SSD/HDD (try shutting laptop off, let sit until fully loaded, then open a Word Processor and time it... close it, then open again... should take LESS TIME since now some is accessed from the DDR3 memory).
VIDEO MEMORY:
If you use the iGPU in the CPU (not a dedicated graphics chip with its own VRAM) then you can change the amount of DDR3 memory it accesses... if playing a light game like Torchlight 1 (or using some non-game applications) you may find it beneficial to boot into the BIOS (how varies such as "F2" on boot or POWER BUTTON plus "F2") then change the amount of VRAM allocated to for example "1024MB" (1GB).
If you have 8GB installed you'd then have just under 7GB available for Windows itself with the other 1GB dedicated to the graphics chip.
Also avoid Ebay. It's known for either peoples problems, fake memory, or poorly made memory.
Other:
way off topic is that "x86" technically does not mean 32-bit. It got used incorrectly so often that even Microsoft uses it interchangeably.
However "x86" refers to the architecture. Really the Instruction Set so that the number "9" means the same thing or some other code (ARM architecture for example has a different Instruction Set).
It's actually:
x86_32, and
x86_64
Meaning the x86 architecture in 32-bit or the x86 architecture in 64-bit.
(SATA vs IDE has a similar path... "IDE" comes from integrating the drive (platters) and the electronics which were separate. So when they did that they becaome IDE HDD's... but the interface was PARALLEL (ribbon cable)... when they changed to a serial interface via SATA cables somehow it became "IDE vs SATA" when it's really "PATA vs SATA" as both drives are still IDE so IDE vs SATA makes no sense...
You can even see ads for "IDE SSD's" ..uh? They mean of course SSDs using the old parallel interface but wow, come on.)"
"now you know... and knowing is half the battle. GEE EYE JOOOOO"