Is re-taking classes at a community college a good idea?

No, I would not re-take it. My first program said not to do this.. I can't remember exactly why, but you should really focus on getting the classes you need. And since you get those grades from a university, getting an A at a community college isn't quite the same as a B :)

How many prerequisite classes do you have left to take? Did you graduate from a 4 year university? What type of nursing program are you hoping to gain admittance to?

A couple of B's are acceptable in my opinion if you have other positive attributes presented in your application. (Also, there is a time limit on many science prerequisite courses that you should be mindful of.)

And, yes, 4 year university courses are generally more difficult. However, when most admissions committee meet, I doubt they scrutinize the transcript to ascertain here is a B in Bio from Harvard and and A in Bio from generic local community college. A cumGPA is a cumGPA.

Since you have yet to take the bulk of the nursing prerequisite courses, I would focus doing as well as possible in these courses and not focus on repeating courses where you earned Bs. I would also take these courses at a community college. I took all of my prerequisite courses that I was missing at a community college and earned As. I actually think it helped my application (and was WAY cheaper than a 4 year institution public or private).

You will want to talk to an advisor who has your transcripts because most universities have a limit on repeat classes. An example would be UTA nrsg dept..they will only allow 4 classes to be repeated. I also think (not 100% sure) that TWU is even more critical of repeats...check their website. An advisor can recommend what path would be most beneficial to you. Hope this helps!

Like tejas said, check with your advisor. My school also has a limit on retaking classes, also you can not take a class for a better grade, if you passed with a C you can not re-take and use the B or A from the re-take. If you fail you can re-take one time for a better grade, with a maximum program wide re-take of 2 classes.