Hi. How to adjust a sweetness of orange upside down cake without a ruining recipe? Thank you.

King Arthur Flour site has a good article (April 2017) on reducing sugar jn 4 methods of cake 10 to 50%.
Have a read, decide which method your orange cake resembles and adjust recipe as they recommend.

If a recipe has 1 cup of flour and 1 1/2 cup of sugar. How to make this cake less sweet?