Situation is:
Currently, I have a repository name phimpme-iOS. I want to capitalize the first letter of the repository, Phimpme-iOS.
When I change the name in Settings > Options > Repository Name, it cannot be changed and it is showing -
The repository Phimpme-iOS already exists on this account
User names and repository names are case-insensitive at Github: phimpme-iOS is the same as Phimpme-iOS; that is, from Github PoV you're trying to rename the repo to an equivalent name.
Try a completely different name — xxx, for example — and then rename it once more to Phimpme-iOS.
Rename your repository to something completely different (e.g. "foo") and then name it back to the original name with the desired capitalization.
来源：https://stackoverflow.com/questions/50092038/how-to-capitalize-the-first-letter-of-existing-github-repository