Can I change a logo that is copyrighted if I change a letter or small detail?

It would have to look different enough so that people would not mistake your logo for the copyrighted one. Otherwise you could be sued.
Changing small details doesn't necessarily avoid copyright infringement.


Answer:
Copyright law protects the artwork or the design itself. And making changes to an existing artwork (or logo) to create a similar one is called a 'derivative work', and is just as protected as the original copyrighted artwork.

Logos are usually covered by trademark law, however, rather than copyright. The goal of copyright law is to protect artistic or creative expression. The goal of trademark law is to protect consumers and prevent false advertising.
your safest bet is to not copy the logo...but if u must u wanna change it as much as u possibly can so you arent violating the copyright

change color , change the size, change maybe the shape a little....but ur best bet is to make it 110% ur own...
no
think if it this way, what do you think Yahoo! would say if you took their logo and just removed the exclamation mark, then said it was yours?
If you know that you are 'changing' someone elses work, that is theft, and in this case, a rights infringement. If you independently come up with a design and someone notices that it is 'similar' to another logo, that is not infringement. Originality of your work is everything.

However similar looking logos for business purposes can be actionable for trademarks, and usualy the first to use the identifying mark in commerce wins.