Learn Spanish (Latin America): Como quiero mejorar, pretendo tener más voluntad. - Since I want to improve, I intend to have more willpower.

Because the person doing the wanting or intending is the same person doing the improving or having. Since the subject doesn't change, you attach the infinitive directly: quiero mejorar (I want to improve) and pretendo tener (I intend to have). You only use que plus the subjunctive when there's a subject change, like quiero que mejores (I want you to improve).

I thought como meant 'like' or 'how.' Why is it used here?

When como is placed at the very beginning of a sentence, it usually means 'since' or 'because.' It sets up the cause or reason for the second half of the sentence: 'Since I want to improve...'

Does pretendo mean 'I pretend'?

No, pretender is a classic false friend! It actually means 'to intend', 'to expect', or 'to try'. Here, pretendo tener means 'I intend to have.' If you want to say 'to pretend' in the sense of faking something, you would use the verb fingir.

Is voluntad related to volunteering?