There are 2 ways to update the theme :

1. You can use Envato Plugin and update the theme by it.

2. Delete the last version of Pinkmart on your Cpanel and add the new one instead of it on the following path :

WordPress installation directory > wp-content > Themes

For the next release, we will add an auto button that helps you update the theme simply.
Also, note that updating the theme will not lose the codes added to the theme setting.

Please try to follow the guideline above and if you were not successful to do it, let me know that I update the theme for you.

Best Regards.