Hi Jean,
This is the right place for this question. Yes, you can remove the older taxonomies if you no longer use them. I only keep some around for reference. Feel free to export them (File | Import/Export | Taxonomies TAB) before removing them in case you ever want to import them again.
You can remove them by selecting the Tax Viewer (Toolbar | Advanced | Taxonomy Viewer), then select the tax list your want to delete from the dropdown; and then click the Delete button to the right.
Jeff |