Nip or cut off the flower heads to stop the plants putting energy into producing seeds (this is called deadheading). The foliage will still be helping the bulbs underground store up energy for next year and if you remove the leaves you may not get flowers next spring. It's best to leave it to die down naturally if you can wait. The foliage will shrivel away over the next few weeks.

You can plant around the bulbs without doing them any harm though. Then, next year your bluebells will come back up then die back as the next 'layer' of plants come through.

Hope this helps, Bob