There are two ways to update CDT 1.x projects to CDT 2.0, after they have been imported, either restart eclipse, or update them using the Convert to C/C++ Make Project Wizard.
Note: the project must first be imported into your workspace using File > Import > Existing Project into Workspace before you can update the project.
For more information on importing projects see Workbench > Tasks > Importing > Importing Existing Projects.
When Eclipse starts, the CDT 1.x project will be detected and you will be prompted to update the project.
Click Yes and the project will be updated.
Select File > New > Convert to a C/C++ Make Project. If that selection is not available, you can find the instructions for adding it here.
From the Convert to C/C++ Make Project Wizard select the project you want to convert and click Finish.
Note: You may need to manually enable Path Discovery for CDT 1.x Standard Make projects, depending on how your CDT project was configured. See Set Discovery Options for details.
Adding Convert to a C/C++ Make Project to the New menu
Set Discovery Options