Directly editing the template files is not recommended. These files may be overwritten during module updates, resulting in a loss of any edits you had made.
Instead, it is recommended to use overrides. Overrides allow you to customise the default template with your own customizations such that they will be preserved through the update process.
To activate a custom template, copy the current used template file and name it "manage_custom.tpl" if using Manager v1 or "manage_v2_custom.tpl" if using Manager v2.
These files are located at /modules/servers/dedicated/