First of all, the performance of notebook depends on the cooperation of various accessories, not just on memory. If other configurations of the notebook are normal, even if the best memory is replaced, there will be no obvious effect, just like the "barrel effect".
Secondly, the memory should be changed according to the situation of the machine. If the machine only supports ddr2,
667 memory, so even if you plug in 800 memory, it only works at the frequency of 667. It is best to replace the memory with the original brand, model and frequency, so that incompatibility is not easy to occur. If your machine has two memory modules, you can buy an identical memory module and plug it into another slot to form dual channels, which is better than replacing it with a larger memory module.