Ideally pick a warm sunny day so that you can move plants and other items out of the greenhouse temporarily.
Move as much as you can out of the greenhouse. Plants in pots, bags of soil and other supplies. Move plants to a sheltered area if the temperature is still cool.
Take a wet/dry vacuum and get rid of any loose dirt, leaves and spiderwebs. Use a stiff brush or broom to loosen any stubborn dirt.
It’s also time to cleanup any winter debris. Not only will it make things look better but also remove diseased materials and reduce pest damage especially from snails and slugs.
You can also touch up any paint that has peeled or wood surfaces that need protection. Use low VOC paints and stains and ensure they are dry before moving things back in.
Once the greenhouse inside has dried a bit, move everything back in. Take your time to also organize and keep things tidy. Wash anything outside before bringing it in.