But changing the width of the section in the middle is not changing. Adapt \textwidth narrows the textwidth but does not allow wider margins.
see next example. So how to adapt the page to for example:
[leftmargin 40mm][middle what is left][rightmargin 60mm] 
this should leave 210-40-60=110mm in the middle, but doesn't.
The textwidth is narrowed but the margins refuse to obey their setting.

yours sincerely
dr. Hans van der Meer

\setuppapersize[A4][A4]
\setuplayout[leftmargin=40mm,rightmargin=60mm,textwidth=110mm]
\showframe
\starttext
setuplayout: leftmargin=40mm, rightmargin=60mm, textwidth=110mm\crlf
abc\dotfill xyz\crlf
\stoptext



> On 22 Nov 2023, at 14:46, Marco Patzer <lists@homerow.info> wrote:
> 
> On Wed, 22 Nov 2023 14:17:29 +0100
> Hans van der Meer via ntg-context <ntg-context@ntg.nl> wrote:
> 
>> I would like to change the width of the margins on the page.
>> In the MWE here, the pagelayout does not seem to obey the
>> \setuplayout command. Why are the margins shown uneffected by
>> \setuplayout?
> 
> Works as expected here. The margins have changed and \showlayout
> gives you:
> 
>  \leftmarginwidth  =  6cm
>  \rightmarginwidth = 10cm
> 
> Change the example to:
> 
>  \setuplayout
>    [leftmargin=6mm,  %% mm, not cm
>     rightmargin=10mm]
> 
> That way you better see the effect on the page.
> 
> Marco