Tell me how to edit the code on the virtual machine?
I don’t have enough information to answer this questions.
What type of OS is the VM?
Did you install the VM or is this the virtual appliance?
What “code” are you trying to edit?
Any changes to the codebase will most likely be overwritten during an upgrade.
I want to change the interface for myself, to add some functionality. I installed a ready-to-use application on VMware without an interface - how do I edit it? can I disable the update?
What functionality are you looking to add?
The documentation for logging into the Virtual Appliance is in the link I provided on Github (http://trudesk.io/v1/guide/installation.html#Virtual-Appliance)
It sounds like you need to fork the project on Github so you have your own copy of the repo. Once you have your own copy you can modify it as you wish and link the VM to your forked repo. No updates will hit your fork unless you update it.