You can rename a file using git's mv command:
$ git mv file_from file_to
Example:
$ git mv helo.txt hello.txt
$ git status
# On branch master
# Changes to be committed:
# (use "git reset HEAD <file>..." to unstage)
#
# renamed: helo.txt -> hello.txt
#
$ git commit -m "renamed helo.txt to hello.txt"
[master 14c8c4f] renamed helo.txt to hello.txt
1 files changed, 0 insertions(+), 0 deletions(-)
rename helo.txt => hello.txt (100%)