Guidelines for Updating other user plugins

I have recently updated 3 old plugins that do not seem to be maintained any longer.

What are the guidelines for posting the updated code? Do I rename it and make it my own (some of them I had to change over half the code) and give credit to the original? Or? Some of these have not been touched since august of last year, others since the beginning of the month. I just want to be sure how I should go about this so I do not get in trouble but still get the code to people who need it quickly.

 

SpriteFight:
You need at least to mention the former author in the credits. On Bukkit-Dev, give him the Former Author Role and so on. Also you should link the profil & original thread.

So, do anything that don't let the plugin looks like its 100% yours!

 

What if it is on git? Do I push the update and if they accept, take my code down? How much code should be redone before renaming / changing author in the plugin.yml?

 

If it's abbandoned you should clone it and update it yourself in your git along with the other points mentioned by mannil.
If you're just gonna make it compatible with the newest build without adding any new features, you could just leave the original author in plugin.yml.