Rclick the dimension and scroll down to display options then pick display as diameter.
Yes, it works,
If you have a circle in a sketch and you dimension it will show as a Dia dimension. If you then trim this circle it will still show as a Dia dimension.
However if t you have a circle and trim it before dimensioning, it will show as a Rad dimension.
Then you will have to do as Martin suggested and right click to change over.
So if you always want to have the dimension shown as Dia then dimension before trimming, if possible.
In lot of cases the diameter is more comprehensive than radius.
My SW learning a bit more complicated vs a newbie due to long Inventor experience.
Thank you for your advises.