Hi friends, how can I update the Guru version without affecting the loaded courses and in the colors I have given.

HI, Pedro.

Thank you for contacting us.
You may use Joomla! Update feature (you need to provide Guru license number) or download Guru installation package and install on top of your existing version.
As for customizations you've made, many depends how you did it.
If you customized core files - they will be overwritten. So first check how they are applied and move them - if needed - to your Joomla! template main CSS file.