Can we change the orbit of a planet...?

...like if we were going to colonize another planet in future, could we for example nudge Mars closer to Earth orbit? or what about something smaller, how about Titan or Ceres? is there something we could do that would affect the gravity of a planet, moon or asteroid enough to change its position (like exploding a big box of nukes!), even if it only made a small difference that would take centuries could we move something that size 50 million miles thru space, like instead of going to other planets can we bring other planets to us?