As the error message itself might suggest, that another template with the same name is already installed. There can also be a possibility that at one time this template had been installed, but not properly uninstalled. In-order to get the template, to work you will have to make sure to totally eradicate or remove the previous template.
The Solutions for this that you can follow are:
Uninstall the previous template.
1.You can do this by logging into your joomla admin then going to:Extensions- ->Install/ Uninstall.
2.Then it will Display the Extension Manager.
3.On the list of the different extension types, select Templates.
4.A list will appear showing all the templates you have installed. This list should show the name of the template that you need to delete.
5.Click the radio button next to it's name, and then click uninstall. The template should be then successfully deleted.
If ever it happens that the template do not get uninstalled properly, then you can log into your account and delete it manually.
You can go to this directory:
Listed here are all the templates you have installed, each with its own directory. The template with the conflicting name should also be listed, click on it, and then delete it.
This should resolve your issue.....