R4 Error

For some reason, I cant get NFS Pro street on my mini SD, it keeps saying invalid: MS DOS Function. Theres 157mb's left of space on it so i dont get why it wont let me copy the file into the drive. And I've tried multiple downloads off this site and none so far worked as well as some other games. Much appreciated for the help.

have you tried reformatting your card?

How would I do so? ._. I'm kinda nub at r4's as you can tell XD