What you are looking for is called a regular expression, or Regex. The basics of Regex-ese is fairly simple and straightforward. Don't get alarmed by some of the more advanced stuff, you (almost) never need the super advanced stuff.
For your Chapter example, I would use:
Find: <p>\s*Chapter (\d+): (.*?)\s*</p>
Replace: [leave blank]
Make sure you have Regex as the Mode and then I would just do them one at a time until you are confident you got them all.
FYI the funny codes are simply wildcards:
Code:
<p>\s*Chapter (\d+): (.*?)\s*</p>
\s* means any (or none) blank spaces
(\d+) means any group of 1, or more, numerical digits
(.*?) means any group of characters before stopping at any space before the </p>
You can find much more in-depth explanation and examples on Regex in the MR Wiki and by doing a search of the threads.
<--->
I'm not aware of a way to select "line 14" and delete it, but if it has a consistent formatting or something that you can use the regex search to find then I'd use that.