For changing the hud size you have to go to minecrafts’ video settings. There you will find a button called GUI Scale.By using GUI scale you can easily change the HUD size.
The HUD is made up of Fitness, Hunger, and User Experience bars, the Easy Access Bar, and a crosshair designating the block or individual that you are currently targeting.
The Interface scale resizes the HUD and Interface in the Options menu, between “big” (3), “standard” (2), and “small” (1). The default value, “auto,” resizes both the HUD and Interface depending on the game window size.
The “Hide HUD” option in Bedrock Edition toggles the active bar, reticle and buttons if you are using the touch controls. Separate choices include hand, paper doll, and coordinates.
The HUD also includes the control screen that can be displayed or disabled using F3, [Java Version only]. Click Shift + F3 to add the additional resource allocation pie map. To view the FPS log, click Alt + F3.
The player can choose to use either his left hand or his right hand. This setting also moves the left slot to the opposite hand.