Can you keep all your upgraded weapons and continue upgrading or do always have to completely restart?

There is a New Game + option that allows you to continue on with all your upgrades, items and inventory.

sweet! ok because i was thinking to myself how i was gonna upgrade all my weapons. Thanks!

Make sure you don't delete saves with a gold star next to them, or youll have to beat the last level for NG+ again to get those saves and play NG +.