unfortunately i have a couple of columns that def need replacement...
a car jack (ie scissor) or bottle jack and a 2x4 or 4x4 should be sufficient to just lift the roof up an inch or two and then swap out the columns. mine are tied into a porch railing so i have to deal with that also.
Recommendations above are correct. Hopefully you don't run into a porch column like our farmhouse. They installed 1" steel dowel pins in the top and bottom. Yeah that made 30 minutes of work into four hours....we were trying to save the posts for another project.