Forms Data Controls :: Copy From One Textbox To Another In Gridview

I have 2 text boxes and a button within an EditItemTemplate field in a simple GridView:

<asp:TemplateField
HeaderText="Text">
<EditItemTemplate>
<asp:TextBox
ID="txtText1"
runat="server"
/>
<asp:Button
ID="bntCopy"
runat="server"
Text="Change"
/>
<asp:TextBox
ID="txtText2"
runat="server"
Text='<%#
Bind("text") %>' Enabled="false" />
</EditItemTemplate>
<ItemTemplate>
<asp:Label
ID="lblText"
runat="server"
Text='<%#
Bind("text") %>'></asp:Label>
</ItemTemplate>
</asp:TemplateField>

how I can transfer the text from the txtText1 Textbox to the txtText2 one when I press the btnCopy button, but preferably in the codebehind so that I can change the text before actually copying?