Jesus didn't change His own instructions regarding murder and adultery. He was correcting the Mainstream Preachers of His time. This is another deception that is further by religious traditions of the day.
Matt. 5:
20 For I say unto you, That except your righteousness shall exceed
the righteousness of the scribes and Pharisees, ye shall in no case enter into the kingdom of heaven.
Jesus is rebuking the Mainstream Preachers of His time. What was Jesus problem with them?
Matt. 15:
9 But in vain they do worship me, teaching
for doctrines the
commandments of men.
Matt. 23:
4 For
they (Pharisees, not God) bind heavy burdens and grievous to be borne, and lay
them on men's shoulders;(Necks) but they
themselves will not move them with one of their fingers.
Peter also encounters this problem in Acts 15. He also rebukes them for the burdens they attempted to place on their necks.
10 Now therefore why tempt ye God, to put a yoke upon the neck of the disciples, which neither our fathers nor we were able to bear?
So Jesus just told us all: Matt. 5:
17 Think not that I am come to destroy the law, or the prophets: I am not come to destroy, but to fulfil.
18 For verily I say unto you, Till heaven and earth pass, one jot or one tittle shall in no wise pass from the law, till all be fulfilled.
Then rebukes the preachers again, for their doctrines, Yes. Then He continues to straighten out their preaching.
21 Ye have heard that it was said
by them of old time, Thou shalt not kill; and whosoever shall kill shall be in danger of the judgment:
There are some, Who come in Christ's Name, who actually preach that this is speaking about Moses, or God (Jesus) who instructed Moses.
But as you can see, Jesus is speaking about the preaching the Pharisees had promoted which had been taught for centuries. When Jesus sent them Prophets to straighten them out, they killed them.
The "Them of old time" are the Levite Scribes, Pharisees who had corrupted God's Word. Jesus exposed what He, as God of the OT, really taught.
22 But I say unto you,
That whosoever is angry with his brother without a cause shall be in danger of the judgment: and whosoever shall say to his brother, Raca, shall be in danger of the council: but whosoever shall say, Thou fool, shall be in danger of hell fire.
You are furthering the preaching that Jesus just amended God's Commandment here, in Matt. 5. But Jesus taught this truth from the beginning and those who aren't interested in "Creating their own religion" as did the Pharisees, can easily find this truth.
Lev. 19:
17 Thou shalt not hate thy brother in thine heart: thou shalt in any wise rebuke thy neighbour, and not suffer sin upon him.
Jesus wasn't changing God's Law here in Matt. 5, as your post implies. He was exposing the Mainstream Preachers and their doctrines which came from man and setting the record straight on what the Word really teaches. You can go down the list and find where Jesus already detailed this truth through Moses. It's just that the Preachers in charge of administering God's Instructions, corrupted it instead. This is why Jesus created a "New Covenant".
Heb. 8:
8 For finding fault with
them, he saith, Behold, the days come, saith the Lord, when I will make a new covenant with the house of Israel and with the house of
Judah: (not Levi)
So will you re-consider your preaching that Jesus changed the murder and adultery law here?