When a demonic or evil entity is encountered you need to exercise caution. These entities are often powerful and have malicious intent. Many types of haunting and activity can be powerful, but these ones have a real mean streak to them.
Demonic entities cannot be 'crossed over'. Instead they must be cast out, or sent back to where they came from. This almost always involves a religious or new age process often involving prayer, blessed water, and a lot of incense. The advantage here is that they don't belong here and are out of place. Knowing that can be a powerful advantage for you.
Of course the biggest hurdle in dealing with a demonic or evil force is what they can do to you psychologically. Morale and faith are always your best friends and in these cases they are the biggest factors that will affect clearing the entity. These entities will try to demoralize and frighten you. Breaking your resolve is what they must do to stop you from casting them out.
While this should go without saying, it is best to leave these situations to those with experience. Many types of haunting and activity can cause harm if they wish to, however, most don't. But a demonic presence does want to cause real harm and it certainly will if it can.