Should a software update crash my MacBook?

I have a MacBook and i cannot access the itunes store because it says i need the latest version of Safari and I cannot install Safari because it says i need to update my Mac Os X software but the last time i tried to update the software my computer crashed and i lost everything and had to reinstall the software and start from square 1. So if I try to update the software to Mac Os X 10.5.8, will my computer crash and give me the blue screen again?

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