Derek Telford, 33, killed James Kerr, 34, over a drugs dispute, at the victim's flat in Glasgow in April 2012.
He was convicted at the High Court in Edinburgh in March 2013 and jailed for life with a minimum term of 25 years.
Telford's appeal against his conviction was rejected but appeal judges ruled his minimum jail term was "excessive".
A written judgement was issued at the Court of Criminal Appeal in Edinburgh on Monday.
Lord Carloway, who heard the appeal with Lady Paton and Lord Bracadale, said in the judgement that Telford was guilty of a "particularly brutal murder in the deceased's own house, using weapons".
He said: "It was also aggravated by the steps taken to conceal the crime thereafter. Accordingly, a very significant punishment part, well in excess of the 16 years...was merited in order to meet the statutory requirements for retribution and deterrence.
"Nevertheless, this was a murder involving a single victim, who did not fit into any special category of vulnerability.
"In all the circumstances, the court does consider that the punishment part selected was excessive. It will quash the period of 25 years and substitute one of 20 years."
Following the trial in 2013, Telford's co-accused Lorraine Callaghan, 41, was cleared of murder.
Both were convicted of attempting to defeat the ends of justice by cleaning up blood and setting fire to Mr Kerr's body.
The murder charge against Callaghan was found not proven.
The court heard how Telford went to Mr Kerr's house in Glasgow's Knightswood area on 11 April 2012 apparently to buy drugs.
He is said to have attacked his victim after being told no drugs were in the house.
The court was told that Telford used a samurai sword, knives and a hammer to inflict 30 wounds on Mr Kerr during the attack.
Pathologists told the trial that Telford had continued to slash at Mr Kerr's face even after he was dead.
He and Callaghan then attempted to defeat the ends of justice by cleaning up blood before setting fire to a pile of the dead man's clothes and burning his body.
Telford also threw Mr Kerr's birth certificate into the flames before fleeing the scene.
A murderer who cut off his dying victim's ear and shouted "can you hear me now" has had his minimum jail term reduced by five years.