I agree with Jura. The preposition 'upon' has the same meaning as 'on' and it is usually used in more formal contexts or in phrases such as 'once upon a time'. You could say: 'I jumped out of bed when hearing loud screams. (or when I heard loud screams)

People don't use " upon" that much nowadays. You just say, I jumped out of bed when I heard loud screams. You can also say, when I heard load screams, I jumped out of bed.

Only problem with that sentence is jump should be in past tense: I jumped out of bed upon hearing loud screams. Upon is usually used as a preposition, meaning it is combined with a noun/noun phrase to modify the sentence. The word itself has a similar meaning to the word "on." Examples, the prepositional phrase of the sentence is in quotes: You will find the city "upon these hills." "Upon his departure," the children proceeded to make a mess.