How to convert a Windows Server 2012 Core to a Windows Server 2012 GUI installation

From the command line we start powershell:
start powershell
Optionally we set a system proxy if we don't have a direct internet connection:
netsh winhttp set proxy proxy.company.com:3128
Then we enter this command so that the actual conversion take place:
Install-WindowsFeature server-gui-mgmt-infra,server-gui-shell
If we can't access the install files from the Internet  then we can use the installation dvd:
Insert installation dvd to the drive and enter the command
Get-WindowsImage -ImagePath D:\Sources\Install.wim
where D: is the dvd drive letter
From there we find the index number of the windows server installation image we have. Using this information we can enter the command
Install-WindowsFeature server-gui-mgmt-infra,server-gui-shell -Source wim:d:\sources\install.wim:2
where 2 is the index number of the installation image we have on our server.
Finally we must restart our server using the powershell command
Restart-Computer
After the restart our server becomes a full gui installation.
To reset the proxy server settings we must enter the command
netsh winhttp reset proxy

How to safely remove a USB disk from a windows server core installation

• On command prompt type "diskpart" and wait for the next prompt and then type "list volume". Take note of the number of your desired volume by watching its drive letter
• Type "select volume x", where x is the number of your USB storage.
• Then type "remove all dismount". 
• Type "exit" to leave diskpart.

How to install .NET Framework 3.5 in Windows 8

In Windows 8 or Windows Server 2012, open a Command Prompt window with administrative credentials (that is, choose Run as administrator).
To install the .NET Framework 3.5 from installation media located in the D:\sources\sxs directory, use the following command:
DISM /Online /Enable-Feature /FeatureName:NetFx3 /All /LimitAccess /Source:d:\sources\sxs
Use /All to enable all parent features of the .NET Framework 3.5.
Use /LimitAccess to prevent DISM from contacting Windows Update.
Use /Source to specify the location of the files needed to restore the feature.

How to enable remoting in a windows server 2012 core

From a command line on the server machine enter
winrm qc
Press y to continue
If the server is not a domain member you can remotely manage it from a workstation adding workstation's ip in wsman trusted hosts using the command:
winrm set winrm/config/client @{TrustedHosts="x.x.x.x"}
where x.x.x.x is the IP address or the computer name of the workstation machine
In the workstation machine enable winrm using the command
winrm qc
and
winrm set winrm/config/client @{TrustedHosts="x.x.x.x"}
where x.x.x.x is the IP address or the computer name of the server machine
After that you can connect to the remote machine using the command
winrs -r:http://x.x.x.x:5985 -u:username "command"
where x.x.x.x is the IP address or the computer name of the server machine, username a user with admin persmissions on the server machine and command the command to execute on the server machine.
Example:
winrs -r:http://192.168.10.10:5985 -u:Administrator "cmd"
For more information take a look at the following post

How to rename the local Administrator account in server core

Enter this command to rename local Administrator account to a new name:
wmic UserAccount where Name="Administrator" call Rename Name="new-name"

In Windows Server 2012 Core we can utilize Powershell, so to find the Local Administrator account name we use the following command:
gwmi Win32_UserAccount | ? {$_.SID -Like 'S-1-5-*-500'}
In order to rename the Local Administrator account to another name we use the following command:
(gwmi Win32_UserAccount | ? {$_.SID -Like 'S-1-5-*-500'}).Rename("New-Name")