TDM version 2.25 is no longer supported and there is no way to purchase a new license for this version of TDM.
If you have models with *.dm2 suffix, you can load them into TDM version 4 directly. If you need to continue with your project, look into your project folder. You will find there *.dp2 file. This file is your project file, is it in fact XML format file and you can find there infomation about files that belong to your project. Additional files in the project folder have suffix DV2. You can rename them to DM2 and load them into TDM version 4.