Making Sentences Clear

I am doing a biology dissertation, and my supervisor said some of my sentences are too long. I understand what I mean, but I sometimes use too many words to explain one idea. I came across best dissertation editing services while looking for ways to improve my writing. What does good editing look like in this case? Should I split long sentences, remove extra words, or use simpler terms? I would like to keep the science accurate while making my writing easier to read. Any practical suggestions would help.