Q.sour oranges how do I get them sweet
I have a potted orange tree that is 4 yrs old. It has giving me oranges every year about the size of a small golf ball but they are real sour. How can I get them to produce sweet oranges?

You may have a calamondin orange or kumquat. These are genetically predisposed with sour taste and cannont be made sweet.
But if you are certain that you have a sweet orange variety then the sour taste could be due in nutrient deficiency and water deficit.
A full range of plant nutrients, adequate water and sunlight are needed to for the process of photosynthesis which makes sugars for metabolism and for storage in the fruit.
There are all purpose fertilizers like the Dr Earth Organic All Purpose on this page:
http://www.fertileearthlandcare.com/domyown/
As well as special fertilizers formulated for citrus like this:
https://www.downtoearthfertilizer.com/products/blended_fertilizer/citrus-mix-6-3-3/and citrus fertilizers like this