what os can i upgrade my imac currently using 10.9.5

Back up your data, check your applications for compatibility, and download High Sierra.

rkaufmann87: See the text in the brackets above.

(177405)

Without know the year of the iMac we cannot answer that question. If you don't know the year, please click the Apple symbol in the upper left of the display and then click About this Mac it will look similar to:

My bad.