Before updating CityTours theme, we recommend you backup your website.
Please confirm you did not change CityTours theme files in your website.
If you did not change theme files, please update the theme with following steps.
1. Download latest version of CityTours theme from https://themeforest.net/downloads
2. Activate another theme ( for example, Twenty Nineteen, etc ) in Appearance -> Themes menu
3. Remove CityTours theme folder in your website ( It is located in /wp-content/themes directory ) using FTP.
4. Install latest version of CityTours theme in Appearance -> Themes menu.
5. Install/Update required plugins in Appearance -> Install plugins menu.
For now, you finished updating CityTours theme in your website.
If you changed theme files, please check readme.txt file in theme package. There is file change log.