In a previous lesson, we learned about how the verb volver can be used figuratively to express the idea of becoming:
 

Después se volvió más profesional

Afterwards, it became more professional

y me encantó más aún todavía, ¿no?

and I loved it even more still, right?

Caption 10, Los Juegos Olímpicos - Adrián Gavira

 Play Caption

BANNER PLACEHOLDER

 
But other Spanish verbs also translate as "to become," for example the verbs transformarse and convertirse (to become, to turn into). These verbs are just as common as volverse but they work differently. That's why you can't just substitute se volvió with se transformó or se convirtió in the example above. When using these verbs you need to be more specific and always remember to use the preposition en (into) to introduce a complement that gives more information about the transformation in question. For example:

...pronto se convierte en una carrera de obstáculos.

...quickly becomes a highway of obstacles.

Caption 41, Animales en familia - La operación de Yaki

 Play Caption

El pergamino se transforma en "cisco" y en almendra.

The parchment is transformed into the leftover "cisco" and the bean.

Caption 41, Una Historia de Café - La Bodega

 Play Caption

You can switch convertirse and transformarse in the examples above and obtain correct expressions:
 

...pronto se transforma en una carrera de obstáculos.
...quickly becomes a highway of obstacles.
 
El pergamino se convierte en "cisco" y en almendra.
The parchment is transformed into the leftover "cisco" and the bean.
 
But with the verb volverse you don’t need the preposition en (into), so you say:
 
...pronto se vuelve una carrera de obstáculos.
...quickly becomes a highway of obstacles.
 
El pergamino se vuelve "cisco" y almendra.
The parchment is transformed into the leftover "cisco" and the bean.

However, to use transformarse or convertirse instead of volverse in the first example you'll have to do more than that, because you can't just say that something or someone se transformó en más profesional (transformed into more professional), right? The expression is incomplete. “Transformed into a more professional what?” people would ask. So you have to say something like:
 

Después se transformó en una actividad más profesional...
Después se convirtió en una actividad más profesional...
Afterwards, it became a more professional activity...

Finally, an interesting tidbit: You can use both transformarse and convertirse alone as reflexive verbs to express the idea that a person transforms herself or himself, without the need of any complement or preposition, but you can't do the same with volverse:

BANNER PLACEHOLDER

Me transformo (I transform myself).
Me convierto (I transform myself).
Me vuelvo (This is incomplete; you have to state what you are turning into, for example: me vuelvo un vampiro, which means "I become a vampire").