It depends.  Usually it's unnecessary to redo academic projects.  Even if you don't like a project overall it's still usually possible to select the best images and only include those.  Most employers aren't all that interested in exactly what the assignment was or in your whole story about how you met the requirements of an assignment - they're more interested in evaluating whether you have some basic skills that will be useful to them.  The images that you select should convey at least a project or two that demonstrate a thought process that leads to completion of something, and items that show good visual design abilities of various sorts, and some basic knowledge of construction and detailing.  Most grads have enough work to show those things without redoing anything - but this question comes up all the time, and it clearly makes some people feel more confidence about their portfolios if they "improve" some projects - so if you're someone who is going to feel very insecure about the quality of your work unless you reinvent it at this point, then it won't hurt anything to do that if you must.

I'm not sure how they would no longer reflect your skills? Have you been designing with a firm already, because if not then your school work is still pretty current so the skills are still relevant even some of the earliest works. I've never heard of someone graduating arch school in Dec though..

If you are just going to look for jobs, then I would choose a few varying project types you did in school. Don't judge them off of each other but rather a good mix of different types of work. (comprehensive, schematic, a model or two, systems, structural design, parametric design whatever you may have unique to your interests) They don't have to be fully developed either, firms aren't expecting you to have a comprehensive knowledge set but rather the ability for development and design strategy. 

With that being said, in terms of redesign on past projects I would say no. Other than a few convention adjustments for drawing presentation I didn't change much in my own portfolio. You can really shape the project how you want so use what you have and just pick out the most successful and useful parts of quickly understanding the project. My studio projects required tons of drawings, models, and diagrams and I eliminated 75% for each and only used what was the best in getting to the point. 

Many architects draw their conceptual napkin sketches after the project’s done, I don’t see why you can’t or shouldn’t make your school projects look the best they can be... go for it, it might not be necessary to get that job or into that program but it will keep you busy doing design for a bit longer before having to do door schedules etc. Enjoy!