Upgrade a weapon at Salty Springs location guide.
One of the week five challenges is to upgrade a weapon at Salty Springs. Upgrade machines can be found all over the map. On the new update of Fortnite you can also carry them in your equipment tab. They can be found from looting chests.
If you can find an upgrade bench there is one located on Salty Springs, on the last house towards Pleasant Park. Exact map location below.