Combining variables; greatest number becomes new variable

I am doing research on colorectal polyps. In my database the size of the polyps is measured both in the pathology report and the endoscopy report; those are 2 different variables. I want to combine these two into one variable, where the greatest reported size out of the two separate variables becomes the size in the new variable. So for example polyp 1 is 10mm in the pathology report and 14mm in the endoscopy report, then I want the new variable to measure 14mm. The variables are numeric. Does anyone know how to do this?

Thank you!

Yes I was trying to use that window, but I cannot figure out to do this using Transform > Compute. I have now done it with this syntax:
COMPUTE max.diameter.poliep.combi=MAX(Grootte_poliep,Poliepkarakteristieken_grootte).
It seems to have worked!