When someone has taken a greater responsibility on a team and done the work that was needed, you can say that they've "stepped up". For example:

Jasper really stepped up and took charge after Tomiko left.

You can't always depend on other people. You've got to step up and do it on your own.

"Stepping up" is always positive.

You can use the preposition "on" with "step up" to explain what someone did:

She really stepped up on the Fall sales campaign.