This script can be used to forcibly remove the v3/v4 versions that typically ship with Windows and update to latest from PSGallery

Invoke-Update-Pester.ps1

#Requires -RunAsAdministrator

$modules = Get-Module -Name Pester -ListAvailable

if ($null -ne $modules) {

    $pesterPaths = (get-item $modules.modulebase).parent.Fullname | Sort-Object -Unique

    foreach ($pesterPath in $pesterPaths) {
        takeown /F $pesterPath /A /R
        icacls $pesterPath /reset
        # grant permissions to Administrators group, but use SID to do
        # it because it is localized on non-us installations of Windows
        icacls $pesterPath /grant "*S-1-5-32-544:F" /inheritance:d /T
        Remove-Item -Path $pesterPath -Recurse -Force -Confirm:$false
    }
}


[System.Net.ServicePointManager]::SecurityProtocol = [System.Net.SecurityProtocolType]::Tls12

Install-Module -Name Pester -Scope AllUsers -Repository PSGallery -Force