1. Remove any fields that may be referenced in other page layouts
2. If you have Chargent Anywhere installed you want to uninstall this package first
3. Remove the Transaction package (Chargent Orders)
4. Remove the base package
Pay attention to any error messages during the process. If you have added Chargent fields to some page layouts, that may cause errors. Salesforce does not want to remove components if they are referenced in parts of your Salesforce configuration (eg in use).
Remove the fields from those page layouts as indicated by the error messages, and remove any other Chargent components from Salesforce.
Salesforce will then allow you uninstall when no Chargent components are in use in page layouts, triggers, etc.