>In options > forms, I ajusted my maximum size form to 800 x 600 as many costumers
>use this resolution
>
>Can adjust it programatically ?
>
>I would lilke to use large forms when programming for myself

If you have a Form's base class you're always using, you can set its properties MaxHeight and MaxWidth to 600 & 800. When you would not be able to make the form bigger, I think, even in design time. I'm not 100% certain, though.