Cross Screen Interaction(Shop screen and Play screen)?

Hi. Im making my first game currently and i have 2 screens, Shop screen and Play screen. In the Shop screen you buy upgrades which should for example make the speed of a bullet larger by +4.

Buying an upgrade is in my shop screen, and the bullet is in the Play screen. How do i make the upgrade on one screen make a change on the other?

BTW for upgrades i am using Buttons with images on them and when you click on it it shoud take 10 of your credits which you  earn by playing the game, and in return incrase the speed of your bullet.

Thanks in advance. Please help me.

use TinyDB

How to pass values from one screen to another screen by  Scott

Thanks man ill give it a go :)