You manage upwards by keeping your management updated on all status, issues, and risks on the project. Let them know what you are doing about it and possible solutions; meet with them on a regular basis and if they are busy and can't see you face to face, at the minimum, send them bulleted status of what they need to know (i.e. something they can read in 30 secs.). Keeping them informed on what's going on puts your stakeholders and managers at ease that the project is under control.