Here I am showing an example of how to delete a module named as testModule from Vtiger 5.0.4.
Simply deleting the files from modules folder associated with a particular module won't delete it completely. But deleting the files is also required. The best way to realize that is, try to reinstall the module, you will get the message that the module exists. In order to delete a module follow the steps given below.
Create a file named delete_testModule.php and put it in the root directory of Vtiger CRM.
Paste the following code into that file delete_testModule.php:
$Vtiger_Utils_Log = true;
$module = Vtiger_Module::getInstance('testModule');
Execute the file delete_testModule.php. Once it is done delete the files associated with the testModule from modules folder in the root directory.