there are two ways,
1.
runtime change form borderstyle
this.controlbox=true;
this.FormBorderstyle=fixedSingle;
2.
create 3 buttons & code it like below
1. maximize put this line in click event
this.Maximized();
2. minimize put this line in click event
this.Minimized();
3. close put this line in click event
this.close();
Happy Coding!
:)