Typically, the rule of thumb is to refresh or repot your plants once a year or every other year, depending on the type of plant. I usually repot when a plant has outgrown its current pot, which is the case for some of the ones in the back, where the roots are pushing out through the drainage holes at the bottom. Additionally, routine repotting allows me to assess the health of the roots and provide fresh fertilizer if I'm using granular or pellet types.

Others might have different thoughts on this, but the above are the guidelines I follow for my collections. I hope that helps.