Mail Taking Up Space

I am having an issue on my Mac. My Mail program is taking up too much space on hard drive. I regulary have to check back on old email for work information. I would like to keep the emails i have in my gmail (which still has plenty of space), but i do not need to access these email in my mail program. Is there a way that i can get the space on my computer back...without losing access to my emails on the gmail website?

Please help.