Updating nuget packages in all projects in a solution

First you have to restore all packages using nuget restore solution_file.sln then update them to latest version by executing nuget update solution_file.sln.

Read more about nuget command line

Updated link to Nuget command line documentation

Nuget Package Manager Console documentation (Visual Studio for Windows)

Edit: Previous link is dead. Added working equivalent and bonus Package Manager Console link.

You have used command line examples, but your question does not state if you require a command line answer. If you do not require command line, you can right-click on your solution in the Solution Explorer, and select Manage NuGet Packages for Solution ... This displays a dialog where you can make your selections. Other than that, you'd need to write a script at this point in time anyway (as far as I know).

As found in NuGet documentation, you can type:

Update-Package

This will :

Update all packages in all projects of the current solution to the latest versions.

To open the Package Manager Console:

Tools > NuGet Package Manager > Package Manager Console

Now, in order to have only one instance of all packages, I have, in my solution folder, a file named nuget.config that contains:

<configuration>
  <config>
    <add key="repositoryPath" value="..\Path\To\My\Packages" />
  </config>
</configuration>

You might need to reload your solution in order to make it work properly.