Can I change attorneys in the middle of my case?
You can, but be cautious about doing so. Most judges don't think much if you change attorneys during the case once, but more than that and they start to wonder if the problem isn't with you and not the attorney(s).
Don't, however, be afraid to change attorneys if you feel you truly aren't getting competent representation. The only thing worse than having to change attorneys is sticking with one who isn't doing his job (and who will eventually lose your case for you).