why wont my ipod update?

iPod touch fourth generation is from 2010, will update as far as iOS 6, and no further.

Here is how to identify the model ➡️ Identify your iPod model - Apple Support

Check for debris in the charging port and gently remove any that might be found there, try a different charging-and-sync cable, ensure your Mac or Windows system and your iTunes (or Finder on macOS Catalina and later) is updated to current, try a different computer, and failing all that then you’re probably headed for a replacement iPod touch or iPhone or iPad as a repair on a vintage fourth generation probably won’t be economical if even available.

And what to do ➡️ If you see error 9, 4005, 4013, or 4014 when you restore your iOS device - Apple Support

Impossible to answer without any details whatsoever.

What iPod model is it? Link-> Identify your iPod model - Apple Support

What iOS is it running?

What happens when you try to update?

Do you get an error? If so what does it say?

Provide some details and someone may be able to answer that question.

That error normally indicates a problem with the USB connection. Try a different cable or port on the computer.

Also, follow the steps here: link->If you see the Restore screen on your iPhone, iPad, or iPod touch - Apple Support