in the subform's design view, take a look at the Caption property of the
Label attached to each control. i'm guessing that the name of the control
matches the Caption of the attached label.

if you want a particular label's caption changed immediately after the value
in a mainform control is changed, then add code to the mainform control's
AfterUpdate event, as

   Dim strCaption As String

   Select Case Me!MainFormControlName
       Case "something"
           strCaption = "x"
       Case "something else
           strCaption = "y"
       Case Else
           strCaption = "z"
   End Select

   Me!SubformCONTROLName!SubformLabelName.Caption  = strCaption

look up Select Case in Access VBA Help, so you'll understand how it works.

hth

If the controls on the form have attached labels, the captions of those
labels override the names of the controls.  So you could change the
captions of those labels at run time. The attached label of a control is
a member of that control's Controls collection.  So you could write
something similar to this example:

   With Me.Subform1.Form
       !ID.Controls(0).Caption = "New ID Header"
       !Desc.Controls(0).Caption = "New Desc Header"
       !Modified.Controls(0).Caption = "New Modified Header"
   End With

(where ID, Desc, and Modified are controls on the form).