Not sure if this application has an MSIuninstaller but if it has one I would recommend using it. For MSI packages, there is an easy deployment step called MSIUninstaller, which provides checkboxes for a silent uninstall. If the software is not an MSI package you will need to do research online to find the exact uninstall procedure and parameters.
"System cannot find the file specified" generally means that there are files referenced in your deployment package that cannot be found by Lansweeper. All of the files (installers, scripts etc.) used in a deployment should be added to a shared folder, so Lansweepr can access them when needed. By default, the Program Files (x86)\Lansweeper\PackageShare folder on your Lansweeper server is shared as DefaultPackageShare$ and you can use that folder to store your deployment files.
We recommend reviewing the package and if possible, manually test each step on a target machine (copy the
Result command of your installer steps and execute it in a command prompt on an example target computer) if possible with the same credentials you are using to deploy. This should help you to identify the cause of the issue.