Dot Com or Dot Net? Always been dot net

I have a site that has been on dot net for about 4 months, no real SEO has been done on it, but it does get some decent rankings.

I recently purchased the . com of my site since it was available, should I be changing over to the .com, or is it fine to leave it on the .net, and just redirect the .com?

IMO, if you change to .com, you are going to start all over again on what you did for .net
Redirection is enough from .com to your .net.

If you 301 permanent the .net to the .com you may experience a delay whilst the search engines update the information., but long term you will be the same as you are now.

If you do it the other way round there will be no change whatsoever, unless the .com already has backlinks to it, in which case you will get the benefit from them too after a delay.