2013 macbook won’t install new MacOS Big Sur

i bought this 2013 macbook air from a pawnshop. it has 500 gb. anyways i’m trying to update it to the MacOS Big Sur update but it keeps getting stuck during the installation part. after it is completely installed it’s supposed to give you the option to restart your macbook but it doesn’t give me that option. i’ve canceled and restarted the update so many times but nothing changes. if you know how to help please let me know what to do !