This is the process to transform (a planet) so as to resemble the Earth, esp. so that it can support human life. A wiki terraforming article suggests methods involving adding greenhouse gasses to increase the temperature of Mars from its unlivable temperature (minus 81 F) to a more Earth like climate.
The problem is not solely based on how far Mars is from the sun, but also it's ability the hold atmosphere as deep as on Earth. This is a result of the difference in the size of Mars compared to Earth. In this case, size does matter. If the temperature was increased, but mass remains the same, you would still need pressure suits to compensate for the thin air. Otherwise it would be like living on top of Mount Everest.
The first order of the process is not to introduce green house gasses(though some are needed), but to increase Mars ability to hold more atmosphere. To do this, Mars needs more mass thus creating a greater gravitational force that is needed to retain the deeper atmosphere.
We are suggesting bombarding the planet with all of the stray meteors found between Earth and Mars. We need to build some device that would sweep all of the boulders floating in space and nudge them into a collision trajectory with Mars. If they were all clumped together, their gravitational force would pull others along with them.