Best practice is to re-install them all. It’s an opportunity to clean house and get fresh updated 24 compliant versions of your extensions. This method helps avoid crashes and incompatible ruby code problems.
However, if you’re feeling adventurous you can copy the Plugins folder from 23 and install it in the correct place for 24 then restart SketchUp. This can sometimes lead to crashing and trouble shooting as sometimes the versions are incompatible but it is possible. Depending on how many extensions you have and what they are this could work fine and save you time.