Help finding a tutorial to alter down a costume jacket Sewing Machines Parts and Sales in Los Angeles

I am altering a costume from an Adult medium to sizes close to a Child Medium. There are 13 costumes (halloween costume) in total not all are that drastic but thats the main ones I am worried about.

I am ok with the vest and pants but was wondering if anyone knows of a good tutorial to alter the jacket? I figured it would consist of me cutting them to panels and pinning but just want something to show me the details.

Thanks!