How to change GitHub account on TortoiseGit

I know it is late but some may find the below information useful.

You need to open the .git folder (it is hidden folder, enable show hidden folders option first) then config file within it.

There you can see many properties like [core], [remote], [origin].

Now you need to create property like [credential].

[credential]
   username = your-account-username
[user]
   name = your name
   email = your email address

if any of the property is already present, replace it with your required account detail.

That's it, now when you commit or push again, it will ask for the password of the account details you have entered in config file.

I suppose you enabled a git credential helper and stored the credentials. You have to delete them manually using the windows credential manager, see https://stackoverflow.com/a/31782500/3906760. After that you will be asked again and can use a different account.