FCKeditor, discontinued after version 2, is the previous version of CKEditor, which started with version 3. The new CKEditor was redesigned from the ground up, offering more features, enhanced security and better integration.
Yes. FCKeditor was discontinued in 2010. Not only does our new version offer more features, it is also more stable and secure. The CKEditor core team has stopped supporting FCKeditor so each new browser update increases the risk of problems with it. It is strongly advised you switch to the latest version of CKEditor. Read more about upgrading from FCKeditor in the Developer's Guide.
The best option is to completely remove FCKeditor and install the latest CKEditor anew. CKEditor is a complete rewrite of FCKeditor with a different folder structure. The CKEditor installation and configuration process is pretty straightforward. If you were able to install FCKeditor you should have no trouble with CKEditor. Read more here.