The .bashrc file is in your user home directory (~/.bashrc or ~vagrant/.bashrc both resolve to the same path), inside the VM's filesystem. This file is invisible on the host machine, so you can't use any Windows editors to edit it directly.
You have two simple choices:
Learn how to use a console-based text editor. My favourite is vi (or vim), which takes 15 minutes to learn the basics and is much quicker for simple edits than anything else.
vi .bashrc
Copy .bashrc out to /vagrant (which is a shared directory) and edit it using your Windows editors. Make sure not to save it back with any extensions.
cp .bashrc /vagrant ... edit using your host machine ... cp /vagrant/.bashrc .
I'd recommend getting to know the command-line based editors. Once you're working inside the VM, it's best to stay there as otherwise you might just get confused.
You (the vagrant user) are the owner of your home .bashrc so you do have permissions to edit it.
Once edited, you can execute it by typing source .bashrc I prefer to logout and in again (there may be more than one file executed on login).