Is it possible to change minor contour to desired value? I need to have major to 3m and minor to 1m, is that possible?

Not directly, no, since minor contours are fixed in relation to the selected major contour interval.
What you could do is generate the map more than once, using different settings, so that you end up with contours on 3m and 1m. You can then keep the contour layers you want/copy to another layer so that they don't get overwritten if you generate the map again.

Ok, that could solve my problem. Thanx!

Also just to note that the only real difference between major and minor contours once they have been generated is in the default styling - minor contours do not show labels, and the line colour is different. You can change this in the layer edit panel, so you could generate on 1m and 3m majors (without generating minors), and then just switch off labels for your 1m contours and style the line width and colour as you see fit.