My laptop ram has more than 50% usage every time

what i have to do to fix it?
also i think one of 2 laptop rams (i have 2 x 2gb)
or maybe 2, are crushed or bad because sometimes when i open it's black screen and to fix it i have to press the open button...
also my cmos is almost dead and i am going to fix it tmrow buy replacing it (i will take my laptop to a store)
every time i open my pc it warns me that firmware has find that cmos has problem...
i should change my ram or motherboard?
and something else..if i can choose to add windows 8 and replace windows 7 should i do it? thnx in andvance
there's a picture to understand better

50% memory usage on a 64 bit OS and 4 GB RAM is quite normal. Memory usage in any modern OS is highly dynamic. The current usage may seem high but that is only there is currently no better use for it. When other applications are started the usage of current processes will be trimmed back, drastically if necessary.

Adding up the items in the memory usage column rarely provides meaningful information and only leads to confusion.

so i shouldn't worry about my ram?
how about replacing windows 7-->8 ?
and what can i use instead of using microsoft security essentials, (a free one?)