Everything I see through my refractor telescope is an inverted upside down image. How can I correct this?

To correct an inverted image, you will need a 90° diagonal lens. When a 90° diagonal is used, the mirror flips the image over, giving a right side up but reversed left to right image. You can achieve a fully corrected image using an erect image prism diagonal. 

These image converters are available from Nipon Scope online store.