How do you get the alohamora spell on Lego Harry Potter years 1-4?

You unlock the Alohomora spell in Lego Harry Potter: Years 1-4 during Year 1 in the Hogwarts Level "Locked Doors".

Here's how:

1. Progress through the Hogwarts level until you reach the area with a locked door that requires Alohomora.

2. Interact with the door and you'll be prompted to learn the spell.

3. Follow the on-screen instructions to perform the spell.

4. You'll then have learned Alohomora and can use it to open locked doors throughout the game.

Note: You may need to complete other objectives within the level before you can access the locked door and learn Alohomora.