How to get, grow and ride a Happy Ghast in Minecraft
To take it off, use Shears on the ghast while nobody is riding it.

Shears are a tool for shearing sheep and collecting delicate blocks.
It is made with the Crafting Table from 2 × Iron Ingot.
Two iron ingots make a pair. They shear wool from sheep, collect leaves, grass, vines, cobwebs and dead bushes as blocks, carve pumpkins, remove armor and harnesses from mobs, and cut tripwires safely. They break wool and leaves faster than any other tool.
2 × Iron Ingot → Shears
// Slots with several items cycle through every accepted option.
To take it off, use Shears on the ghast while nobody is riding it.
Shears take the armor or the Saddle off again.
Kill 3 sheep (1 Wool each), or shear them if you have Shears (1 to 3 Wool each).
Shears take the saddle or the armor off again.
At the Crafting Table: 2 × Iron Ingot give 1 × Shears. It can be found as loot in Abandoned Camp and Village. Sold by Villager: Shepherd (Novice).
It shears sheep and collects leaves, grass and webs. Use it on: Sheep, Mooshroom, Snow Golem and Bogged.
238 durability points: each use removes one, and it breaks when none are left. Mending and Unbreaking can extend it.
No: only one per inventory slot.
4 enchantments: Efficiency, Mending, Unbreaking and Curse of Vanishing.