Hi,
Is there a digit missing from the Windows recommended? I would be surprised that Windows is only recommending 1.8GB
I would go for the larger of the two, it is a small amount of disk space to tie up.
Windows will use only what it needs anyway, up to the amount you have set.
In addition, have a look at the Startup apps and programs running in the background.
you can disable startup apps in Task manager,
right click on Start and select Task manager
select the Start-up tab
on each app you don't need running from windows start, right click and select Disable.
if you need to enable it again, go back, right click on it and select enable.
Do not be tempted by any of the many adverts for memory booster software or speedup tools - at best they are snake oil and could cause more issues than they solve.