Using a ramp
...I agree with Teresa, be patient. Once they get the hang of it, there'll be no stopping them. When I installed the second level of my cage, Squeaky took a couple of weeks before he felt comfortable going up and down. I had to coax with a food trail. What helped the most, however, was his young male guinea pig buddy (who ran up immediately, and has a tendency to jump off half way down - so I've added an extra layer of bedding to soften his landing). Once he'd seen the youngster handle the ramp, Squeaky was off and running.