In most cases drapes get dusty but not dirty so a good vacuuming with the small flat attachment for furniture should suffice.
If they come off, throw them in the dryer on air fluff. Done. Rehang. Don’t let them sit in the bottom of the dryer when they are done.
All drapes or curtains can be removed for cleaning. Send a photo. We can tell you how to take down. In my house, curtains and drapes get filthy. I have doors and windows open any chance I get. Plus I have a houseful of rescue pets. They need to be cleaned several times a year or on an as needed basis. Vacuuming drapes will get you through a short term cleaning.
vacuum thoroughly and use a fabric spray cleaner on them also freebrez for fabrics will make them smell fresh and clean