At the instant you captured with top, there was plenty of memory and you were not heavily using the CPUs.
If you caught it at a moment when it was "slow" then the problem is certainly something other than CPU or RAM.
If you caught in nearly idle in between times when it was slow, maybe the limiting resource is CPU. Not likely RAM.
My guess based on that top data, plus your statement "my site is very slow for the last few weeks" is that the problem is in the network connectivity, not in the processing internal to that system.