Like in your hero alter? Where are you trying to remove your higher level hero from?
I read your Heading, You need to make sure of a few things before "deleting a hero". Basically you need to remove the heroes crest, remove them from any areas they are used (this is usually underneath the heroes picture while on that heroes profile). After that you will be able to consume the hero. Once consumed there is no reversing it so make sure you are sure you want to get rid of him. You consume the same way as you would consume a slime.
I am courious, who are you consuming? And Welcome to the wikia, if you need anymore questions answered just ask or look around :)