Check this article for a common actions list: https://nwdthemes.com/2016/07/12/magento-2-uninstall-module/
- remove the folder app/code/Nwdthemes/Powerbanners
- drop module tables from database1234DROP TABLE IF EXISTS `nwdthemes_powerbanners_style`;DROP TABLE IF EXISTS `nwdthemes_powerbanners_banner_store`;DROP TABLE IF EXISTS `nwdthemes_powerbanners_banner`;DROP TABLE IF EXISTS `nwdthemes_powerbanners_slider`;
- remove the config settings1DELETE FROM core_config_data WHERE path LIKE 'nwdthemes_powerbanners%'
- remove the module from app/etc/config.php
- remove the module from database table setup_module1DELETE FROM setup_module WHERE module='Nwdthemes_Powerbanners'
- flush cache1php bin/magento cache:flush
- recompile code if you are in production mode1php bin/magento setup:di:compile