change another window's size

Can I change another window's width and height from my VB application If I know the caption on that window?
Thanks

Yes you can

VB Code:

' Code on Form1
  Form2.Show
  Form2.Width = Form2.Width - 500
  Form2.Height = Form2.Height - 500

With caption name

VB Code:

' Code on Form1
    Dim strCaption As String
    Dim MyObject   As Form
    
    Form2.Show
    strCaption = "Form2"
        
    For Each MyObject In Forms
        If MyObject.Name = strCaption Then
           MyObject.Width = MyObject.Width - 500
           MyObject.Height = MyObject.Height - 500
           Exit For
        End If
    Next

If you want to change the size of a external applications window then:

If you only know the caption (not the class) then you'll have to enumerate through the windows using EnumWindows, and check the window caption using GetWindowText, until you find the right one.

If you know the window class as well as the caption then you can use FindWindow to get the handle.

Once you've got the handle of the window you can use SetWindowPlacement or MoveWindow (and there are probably others) to change the windows position and size.