Yes, you can edit files directly from the Webmin file manager. It's not immediately intuitive how to do it though, so here is an illustrated tutorial.
If you're familiar with cPanel or another Linux server control panel for VPS, Webmin's interface isn't quite as clear but rest assured it's easily possible to edit files in Webmin. You won't need to download and upload files or install any additional software on your server.
Webmin is a popular choice of free open source control panel - it's well established and it handles a wide range of tasks beyond simply editing files. It can handle log file rotations, cron jobs, and much more. The main downside is that its interface and user experience is not quite as straightforward as that of some proprietary control panels such as cPanel. If you don't yet have a control panel installed on your VPS and you need to get started with something, I recommend Webmin because it's free, easy to install and lightweight - it doesn't have many dependencies.
This tutorial uses version 220.127.116.11 of Webmin, the latest version at the time of writing.
1. Log into Webmin
It doesn't matter whether you have a privileged or non-privileged account, start by logging into Webmin on your server.
2. Go to Tools > File Manager
After going to Tools > File Manager, your screen should look like this:
You're able to navigate between different directories via point and click. Locate the file of interest that you want to edit.
3. Click on the 3 dots next to the file icon
Once you're in the directory containing the file you want to edit, click on the 3 dots next to the icon of that file. The dots only show up when you hover over that file name, so don't worry if you can't see any dots when you first see the directory listing.
Do not click on "File" or "Edit" in the upper menu, even though it looks like you should do it - don't! You want to click on the 3 dots as shown in the screenshot below:
Here is the same image magnified below:
After you click on the 3 dots, an additional menu will come up for that particular file, as shown below. Simply click on "Edit" and you'll be able to directly edit the file.
You can easily edit files from within the Webmin file manager, as shown in the tutorial above. The Webmin interface is not as intuitive as for other Linux VPS control panels but be assured it's easily possible to edit files directly in Webmin.
If not all of your Linux users have access to Webmin yet, take a look at our tutorial on how to allow an existing Linux user to log into Webmin on your VPS.