I just started, what should I upgrade bext

Honestly, pass blocking is so important in this game. Alex Mack as a team captain would make a great upgrade for you at Center. Center is where I would start so if there's a different player you like, you can go that route. Also, you need to upgrade Mike and Safety. If you can great a great safety, you can use him at sublb as a "user" player. You could also use a mike there like Tremaine edmunds or Jerome baker as a budget option.