Hope you know that files in Unix are case-sensitive. So first thing is, why did you mention filenames in lower case when they are originally in Upper or mixed cases?
Anyway, you can translate lower with upper and vice-versa (but I will do it for whole file).
~$ cat makefile | tr '[[:upper:]]' '[[:lower:]]'
If you want to for only some part of the file, then share that snippet.