What chat software are you trying to use?
Is it a website, or a program (that most likely contains adware or spyware... which is why it may be blocked)
Its not recommended that you lower your Firewall protection. If you cannot get to a chat room because of Parental Content Filters, then find the administrator of the PC (whoever installed the parental control software) and ask them to allow you.
If it is a program, you can allow it by going into the Firewall settings, and click "add program" or "allow program" under "Trusted applications/programs" (or anything similar to this) and searching for the application you want to use.