When you upload a file, Google Drive automatically creates new versions if it is already available. This is a very nice approach to keep backup files in history by 30 days but it causes much more space requirement in your drive. You can remove unwanted backup files by following steps;

• Go to Google Drive,
• Click the file you want to manage,
• Click on the three dots menu to expand it and select manage revisions,
• You can delete the unwanted backups from here.