>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

I set my maximum size to none in Options.

Then I can make my form any size by dragging or by setting height and width properties.

You can set form size (height and width properties) at runtime as well.