Exactly how depends on the "relationship" between the two forms.
Have a look at these, one of them will fit your circumstances.
The form that creates an instance of another:
MyForm mf = new MyForm();
mf.Show();
Is the "parent", the other form is the "child".
(This doesn't imply any formal MDI relationship)
Transferring information between two forms, Part 1: Parent to Child[
^]
Transferring information between two forms, Part 2: Child to Parent[
^]
The code is in C#, but it's pretty obvious, and an online translator like
Code Converter C# to VB and VB to C# – Telerik[
^]
Transferring information between two forms, Part 3: Child to Child[
^] will help with anything you don't understand.
And you do realize that variables are not preserved from run to run of your app? So unless you save your new password somewhere - a file, a DB, whatever - the changes they make will not be applied next time they run your app?