Except when it says to gather your friends and go out killing.
First of all, we must differentiate between murder and killing. Hebrew also has two different words, one is for murder and one for killing.
To simply put it, murder is illegal killing. There is legal killing, you can kill an animal in order to eat, you can kill a person in self-defence for example someone attacks you with a knife and you defend yourself, or someone pulls a gun on your family, you don't just stand there and do nothing. You can also kill someone by an accident. Even in courts they are looking if there was an intent.
Murder is killing with an intent.
Now let's look at God's commanding Israel that all Canaanites should be killed.
(If you claim that there's no God, why is any Old Testament 'atrocity' wrong? Many claim that God of the Bible is immoral, and if you are atheist, there is no moral standard, it's just your opinion).
Is God arbitrary or does He give reasons for judging people in Old Testament? He gives reasons. He doesn't just wake up like a mob boss and go 'Canaanaties, I want them all dead'. He's got reasons for it, and probably the biggest reason after 400 years of warning, is that the Canaanites were sacrificing children on molten hot idols. So God saw this evil, gave them chance to repent of it and stop, but they did not, God said ok that's enough, time to stop this evil practice of killing children, so He sends Israelites to put an end to this evil.
Does God commit murder by ending lives on Earth? No, because He is the creator of life, He does not murder anyone, so when He takes life, that's up to Him, He can resurrect life, we cannot do that, so if God wants to take someone's life, He absolutely can.
Israel was God's chosen nation, His people, He commanded them to be holy, to be separated from all the evil, so He commanded to destroy evil so they would stay holy. That does not mean they could go out whenever they wanted, only when God commanded them.
It's like when there was rise of evil in WW2. Many nations and people gathered together to stop this evil.