8GB RAM and 64bit OS not showing up

Hello,
i recently got a toshiba satellite pro laptop, and its got 8gb ram and can use 64 bit OS
however,when i look at systems settings on my windows 7 home premuim, it says its only 2.87 gb ram, and 32 bit OS
How can i get my 8 gb of ram and 64 bit OS back, please?