You can change your characters height in game by using command /character set height <scale> (per character). Here's a helpful list to determine your in-game scale based on your character's height.

Example: if your character is 4'5, then do /character set height 0.75

• Minimum height: 0.25 (1.35 blocks tall - 4 ft 5)
• Default Height: 1 (1.8 blocks tall, 5 ft 11)
• Maximum Height: 1.25 (2.25 blocks tall, 7 ft 5)

The below chart is not a rule or requirement, simply a guide!