8gb of ram would be better.
It would also let you run in faster dual channel mode and improve performance of integrated graphics.
Otherwise, I think I would use a 32 bit version of windows 10 .
It takes less resources than the 64 bit version.
Windows 10 can use compression to keep ram usage low. A benefit that 7 does not have.
If you have not yet done so, replace the HDD with a ssd.
It will transform the performance of the laptop.
I have done this on several old lenovo units.
Memory usage stats are hard to interpret.
Windows keeps unused code in ram in anticipation of fast reuse.
The key is how much is needed when your apps are running.
Windows task manager hard fault page rate will tell you if you need more ram.
If you see a hard fault rate of 1 per second or more, you probably need more ram.
If you have a ssd for the page file, such hard faults will get resolved some 40x faster.