install

Set-ExecutionPolicy Bypass -Scope Process -Force; iwr https://community.chocolatey.org/install.ps1 -UseBasicParsing | iex

Upgrade

choco upgrade chocolatey

uninstall

If you also intend to delete the Chocolatey directory, remove the -WhatIf:

Remove-Item -Recurse -Force "$env:ChocolateyInstall" -WhatIf
[System.Text.RegularExpressions.Regex]::Replace([Microsoft.Win32.Registry]::CurrentUser.OpenSubKey('Environment').GetValue('PATH', '', [Microsoft.Win32.RegistryValueOptions]::DoNotExpandEnvironmentNames).ToString(), [System.Text.RegularExpressions.Regex]::Escape("$env:ChocolateyInstall\bin") + '(?>;)?', '', [System.Text.RegularExpressions.RegexOptions]::IgnoreCase) | %{[System.Environment]::SetEnvironmentVariable('PATH', $_, 'User')}
[System.Text.RegularExpressions.Regex]::Replace([Microsoft.Win32.Registry]::LocalMachine.OpenSubKey('SYSTEM\CurrentControlSet\Control\Session Manager\Environment\').GetValue('PATH', '', [Microsoft.Win32.RegistryValueOptions]::DoNotExpandEnvironmentNames).ToString(),  [System.Text.RegularExpressions.Regex]::Escape("$env:ChocolateyInstall\bin") + '(?>;)?', '', [System.Text.RegularExpressions.RegexOptions]::IgnoreCase) | %{[System.Environment]::SetEnvironmentVariable('PATH', $_, 'Machine')}

If you also intend to delete the tools directory that was managed by Chocolatey, remove both of the -WhatIf switches:

if ($env:ChocolateyBinRoot -ne '' -and $env:ChocolateyBinRoot -ne $null) { Remove-Item -Recurse -Force "$env:ChocolateyBinRoot" -WhatIf }
if ($env:ChocolateyToolsRoot -ne '' -and $env:ChocolateyToolsRoot -ne $null) { Remove-Item -Recurse -Force "$env:ChocolateyToolsRoot" -WhatIf }
[System.Environment]::SetEnvironmentVariable("ChocolateyBinRoot", $null, 'User')
[System.Environment]::SetEnvironmentVariable("ChocolateyToolsLocation", $null, 'User')