How to access parent forms textbox.text on child form?

Question

I have 3 forms in my application, a login form, a main menu, and the form to open from the menu. When the user logs in, the username and password are stored in  two public strings in the login form. When they navigate to the main menu and select the page to open, they create a text file by inputting information. Once the select the finish button, the text file is created and is uploaded to a server to store. In order to upload to the server, i need to pull the usernmae and password from the login form. How do I accomplish this?