Help Connecting to WiFi IP

So I've been using the free public WiFi to connect my laptop at work for about 6 months (we can't hook them up here). Today I get a message that another computer is using my IP. I know how I would go about resetting my router if I had control of it and all that, but how do I deal with this when I have no access to the the router or access point?

Thanks in advance. I'm using a Macbook Pro on the latest updated OS.

(I'm a brand new Mac user, FYI; just converted from PC).