Connect to your Office 365 instance.

$UserCredential = Get-Credential
Connect-MsolService -Credential $UserCredential

Show your license SKUs




Run the command to change your user's licenses All At Once (example is from Office 365 Education for students to  Office 365 Education Plus for student )

get-MSOLUser -All | where {$_.isLicensed -eq "TRUE" -and $_.Licenses.AccountSKUID -eq "[School]:STANDARDWOFFPACK_STUDENT"} | Set-MsolUserLicense -RemoveLicense "[School]:STANDARDWOFFPACK_STUDENT" -AddLicense "[School]:STANDARDWOFFPACK_IW_STUDENT"


10 At a time (Test it)

get-MSOLUser -All | where {$_.isLicensed -eq "TRUE" -and $_.Licenses.AccountSKUID -eq "[School]:STANDARDWOFFPACK_STUDENT"} | select -Last 10 | Set-MsolUserLicense -RemoveLicense "[school]:STANDARDWOFFPACK_STUDENT" -AddLicense "[School]:STANDARDWOFFPACK_IW_STUDENT" 


Note: It takes a long time to finish.  I ran it on about 2800 students and it took around 45 minutes to complete.