You won't clean the sealant off. You are going to have to identify what type of sealant has been used if you want to repair the bare patches. Cleaning will be no problem. Acrylic sealant will soften and dissolve with xylene but the better sealants won't. Never ever try to reseal with a different type of sealant as I will end in tears, resiblock say it can be done but I have a different view. You will need good weather if you want to seal anything at this time of year. If I were you I'd steer clear of sealing without doing a course