to take action when there is a need or opportunity for it

Investors have to step up and assume more responsibility for their assets. 投资者必须采取行动，为他们的投资承担更多责任。

to increase the size, amount, or speed of a process that is intended to achieve something

The police are stepping up their efforts to fight crime. 警方正在加大打击犯罪活动的力度。

Security has been stepped up at the airport. 机场加强了安全措施。