The amount of risk depends on a lot of factors.
1) Is that server or the FTP service visible from outside of your network?
2) What kind of information is on that server?
3) If it goes down, what impact does that have on your day-to-day operations?
4) What kind of permissions do you have set up on the FTP directory?
5) What FTP verbs do you allow?
Without more information, it's really hard to know. If you don't know the answers to these questions, though, I'd say it's too big of a risk to take.