Delete every other line in notepad++

You can try to use a Macro.

1. Start recording Macro
2. Press down n-times
3. Press Shift+End
4. Press delete two times
5. Stop recording Macro
6. Run Macro until end of file

I'm not sure Notepad++ is the best tool for this, but using the Power of Regex, we should be able to do it.

Open the replace menu, fill in ([^\n]*\n)[^\n]*\n in the "Find what" box and $1 in the "Replace with" box. Then select regular expression for the search mode, click replace all and every second line is deleted.

You can build similar regexes if you want to do something similar. For example, (([^\n]*\n){a})[^\n]*\n will replace every nth line if you replace a by n - 1 and [^\n]*\n([^\n]*\n) will let you keep even lines instead of odd ones.