This paper describes experience gained and lessons learned from restructuring OODesigner, a Computer Aided Software Engineering (CASE) tool that supports Object Modelling Technique (OMT). This tool supports a wide range of features such as constructing the three models of OMT, managing information repository, documenting class resources, automatically generating C++ and Java code, reverse engineering C++ and Java code, searching and reusing classes in the corresponding repository and collecting metrics data. A version 1.x of OODesigner has been developed for 3 years since 1994. Although this version was developed using OMT (i.e. the tool has been designed using OMT) and C++, we recognized the potential maintenance problems that originated from the ill-designed class architecture. Thus that version was totally restructured, resulting in a new version that is easier to maintain than the old one. In this paper, we briefly describe the tool's functionality, its development process and its refactoring process, emphasizing the fact that the refactoring of the tool is conducted using the tool itself. Then we discuss lesson learned from these processes and we exhibit some comparative measurements of the developed versions.