You can remove the terms which you no longer need in your localization project in several ways.
How to remove terms in the user interface
To remove obsolete term from your localization project, you can import an updated version of your source file using the Import Terms functionality in the Project Page. After importing the updated file, the system will prompt you and ask what you want to do with the terms which exist in the project but do not exist in the file you just used to import terms. Just check the terms you want to remove and then press Deleted Selected.
You can also remove terms in the View or Add Terms page. Just check the box next to the terms that you want to remove and then, at the bottom of the page, choose Delete Selection and press Go.
With the GitHub, Bitbucket, GitLab or VSTS integration
To remove oboslete terms from your localization project using an integration with a code hosting service, you can run a webhook with the sync operation.
We strongly recommend that you do not use the sync webhook if you have multiple files linked to the source language. The sync webhook deletes the terms which are in the project, but are not in the connected file. So you may end up losing terms you imported from other files. The terms from the file last synced is what remains in your POEditor project.
How to remove terms using the API
When working with the API, you can use the projects/sync method to remove all the obsolete terms at once. If you do not want to delete all the obsolete terms, you can customize what terms to delete with the terms/delete method.
Note: When you remove a term from a project, you also remove all its corresponding translations. In case you add the term back to the project, you will be able to recover its translations using the Translation Memory feature.