It is hard for a lot of people when they start meditating. If you can cross your legs, it's recommended, however it is not necessary. If you do insist on crossing your legs, that would be fine, because when I first start meditating, i would get horrible leg pains and it kills me, but i take it slowly and after a while, I became more..flexible or used to it I guess but I only do half-lotus position nowday. But if you do cross your legs, and when you feel pain you should definitely release your foot from crossing position and can just put it down like you would be sitting on a chair. Just make sure to keep a relaxed-straight back and concentrate on your breathe counting or w.e. meditation you are doing.
Wherever you are, that is where the mind should be. Always be mindful, and be your own master. This is true freedom. - Grand Master Wei Chueh