This is a tense difference
Past tense - previously I wanted to be something. You may or may not still want to be that thing
something is what I wanted to be
When I was a child, I wanted to be an astronaut
Future tense (typically hypothetical) - in a certain circumstance, this is what you would like.
I would want something
If I was hungry, I would want some soup
Or Future tense but this time not hypothetical. This is what you are going to want, regardless of circumstance
In future I will want something
Later tonight I will want to sit down and watch a film
And the one you didn't include Present tense. Right now, you want this.
I want something
I want a chocolate
Although remember that "want" is referring to the future. So even in the present tense you're talking about what you would like to happen either in the immediate or distant future.