In my name shall they cast out devils
Casting out devils all believers can do. But it should be done in faith and not by sight.
(II Corinthians 5:7 [KJV]) (For we walk by faith, not by sight:)
If you do it by sight without faith then you might fail and get attacked by the unclean spirits.
(Acts 19:13-16 [KJV])  Then certain of the vagabond Jews, exorcists, took upon them to call over them which had evil spirits the name of the Lord Jesus, saying, We adjure you by Jesus whom Paul preacheth.  And there were seven sons of one Sceva, a Jew, and chief of the priests, which did so.  And the evil spirit answered and said, Jesus I know, and Paul I know; but who are ye?  And the man in whom the evil spirit was leaped on them, and overcame them, and prevailed against them, so that they fled out of that house naked and wounded.
We can move mountains by faith if we have the faith of a mustard seed. So then we can also cast out unclean spirits by faith.
(Matthew 21:21 [KJV]) Jesus answered and said unto them, Verily I say unto you, If ye have faith, and doubt not, ye shall not only do this which is done to the fig tree, but also if ye shall say unto this mountain, Be thou removed, and be thou cast into the sea; it shall be done.
In fact we can walk on all the power of the enemy by faith through prayer in our closet.
(Luke 10:19 [KJV]) Behold, I give unto you power to tread on serpents and scorpions, and over all the power of the enemy: and nothing shall by any means hurt you.
Make Jesus marvel by having greater faith than he has found in all of Israel.
(Matthew 8:10 [KJV]) When Jesus heard it, he marvelled, and said to them that followed, Verily I say unto you, I have not found so great faith, no, not in Israel.
When you cast out devils you do the following. This is a prayer template.
In the name of the Lord Jesus Christ I command all you unclean spirits to depart from John Doe now.
It can be varied a lot. Like putting in more exact information, like street address of the building or person. It can also be varied to casting out all unclean spirits from all people in a certain building or working in a certain corporation etc.
But when you cast out unclean spirits it is sometimes good also to bind the spirits so that they cannot enter the person or animal again for a specific period.
In the name of the Lord Jesus Christ I bind all you unclean spirits to not enter John Doe again, starting now continuously lasting for 24 hours.
Unclean spirits can enter all living things that don't have the Holy Ghost in it. So they cannot enter saved believers but they can still affect saved believers through other people or animals.
Some connect unclean spirits to disease. I would say that there are many diseases that are not caused by unclean spirits, infirmities of the flesh that are caused by sin rather than unclean spirits, for example fornication or violence or smoking can cause infirmities in the flesh. The wages of sin is still death in the new covenant.
(Romans 6:23 [KJV]) For the wages of sin is death; but the gift of God is eternal life through Jesus Christ our Lord.
The strength of the sin is the law.
(I Corinthians 15:56 [KJV]) The sting of death is sin; and the strength of sin is the law.
Unclean spirits can even do miracles.
(Revelation of John 16:13-14 [KJV])  And I saw three unclean spirits like frogs come out of the mouth of the dragon, and out of the mouth of the beast, and out of the mouth of the false prophet.  For they are the spirits of devils, working miracles, which go forth unto the kings of the earth and of the whole world, to gather them to the battle of that great day of God Almighty.
You can cast out unclean spirits of anyone that is bothering you.
If you cast out unclean spirits of a saved person or a person that does not have an unclean spirits you will not be hurting the person because the prayer is not against the person it is to cast out the unclean spirit. Also casting out an unclean spirit from a person is never an evil act in the bible. In fact its doing the will of God.
However its not recommended to cast out unclean spirits form a person in front of them because that can if you are unlucky end you up in court. Rather do it in prayer in your closet. Also you do not have to inform the person that you are casting out unclean spirits from the person.