I'm beginner as well but I'll try to help. You have less than 24 degrees and greater than 24 degrees there. May want to add less than or equal to 24 degrees. Once its 24 degrees exactly what would happen?
if (temperature <= 24)
For clearing the hot hot hot you simply set the cursor to where you need to and
lcd.print(" ");
Just prints spaces. Was this what you're trying to do? Remember that when you want to print the hot hot hot you'll need to set the cursor back to the correct position.
@arrch good call haha! I missed your post.
I'm not sure if there's a better way to do that but it works. Hopefully someone else with more experience can chime in. 