Many beekeepers replace the queen approximately every 2 years. There are many reasons to replace the queen including:
Queen failed and there is no queen present
Very few or no eggs and lack of young brood in the colony
Queen has a poor laying pattern or “shotgun brood pattern”
Prevent supercedure (bees replace the queen themselves)
Colony temperament or seeking more hygienic, disease resistant bees
Making splits to increase apiary or avoid swarming
Old queen, part of routine colony maintenance
If a colony is not thriving then replacing the queen may improve the condition of the colony. If you believe that your hive is diseased, it should be treated before replacing the queen. Some beekeepers replace the queen of overly defensive or aggressive colonies with a queen that has a calmer disposition.