Adapting a comic book into a TV series is never going to be an easy task, but making changes from the source material is sometimes necessary to make the adaptation possible, or to improve on issues of the original story.
The Walking Dead started out as a very faithful adaptation, but as the series has progressed it has gotten further and further from the original vision seen in the comic series.
Some of these changes are great: as many people know, Daryl doesn't feature in the comics, and he has gone on to be one of the most recognisable characters of the entire show.
Other characters, such as Carol, are unrecognisable when compared to their comic counter-parts as well. It's good to keep things fresh for the comic readers, and exploring alternate story arcs can allow for the characters to grow in interesting ways. The Grove is one of the best episodes of The Walking Dead, and we wouldn't of gotten it without Carol's character being changed.
Sadly, not all character changes are good. Sometime the writers stumble and just accidentally end up making them less likeable, or they make them make poor decisions that don't feel right for what that character is supposed to be. With The Walking Dead, it's usually a flip of a coin.