Learn Polish: To jest szansa, aby powiększyć nasz zespół.

It is built from większy (bigger), which is the comparative form of duży or wielki. As covered in this lesson, adding the prefix po- turns a comparative adjective into a perfective verb of changing size, literally meaning 'to make bigger' or 'to enlarge'.

Why do we need the word aby here? Can't we just say szansa powiększyć like the English 'chance to enlarge'?

Unlike English, Polish strongly prefers not to attach an infinitive directly to nouns like szansa (chance) or okazja (opportunity). Instead, you use a conjunction of purpose, like aby or żeby, to bridge the noun and the verb smoothly.

Is powiększyć perfective or imperfective, and why is that aspect used here?

It is perfective, with its imperfective pair being powiększać. It is used here because the sentence focuses on the final, completed goal of achieving a larger team, rather than the ongoing process of growing it.

Why doesn't nasz zespół change its endings if it's the direct object of the verb?

It actually is in the accusative case, which is required by the verb powiększyć. However, because zespół is a masculine inanimate noun, its accusative form is completely identical to its nominative form.