I colored my hair a medium golden brown and it turned out to dark. Any suggestions to lighten it a little.

Get highlights or even get it dip-dyed or get an all over shade at the hairdressers of your preferred shade

You could get some highlights but they should be done professionally. The only thing that will lift a permanent colour is bleach so unless you want to pay for highlights or it was a semi permanent colour which will wash out you are stuck with it, sorry.