If an update is available and you are going to install a newer version of the template, you must perform some actions.
Kunena template comes with empty params.ini file where all settings are stored.
Here is the file:
components/com_kunena/template/name_template/config/params.ini
Copy this file somewhere on your HDD via FTP manager and upload a new version of the template. If you added some custom styles to custom.less file, you need to backup it too (see below).
How to install the update:
Go to Administrator Panel > Components > Kunena > Templates, click on New Template and upload the installation package.
After the update replace empty params.ini to your params.ini file from the local folder. Now go to Administrator Panel > Components > Kunena > RoundTheme template and make sure that all params are correct and then click on Save.
New settings file will be created with possible new params which could be added to the new version of the template. Also bear in mind that CSS file will be rewritten after saving the settings. It is highly recommended to clear both Joomla cache and browser cache.
Custom styles
Kunena template comes with empty custom.less file which is located here:
components/com_kunena/template/name_template/assets/less/custom.less
If changes were made to this file, you also need to make a backup of the file and replace it after the update.
Alternative method
You can unzip the archive and remove the following files:
name_template/assets/less/custom.less
name_template/config/params.ini
Then make archive again and install the distribution package. As a result, no overwrite will be taken.