Update a theme via FTP
You will learn how to update your theme using the FTP client FileZilla.
I'll use the theme Bazar for this example, but it will be the same for all other themes.
Before to do the update, is ALWAYS a good idea to make a backup of your actual website.
Download FileZilla Client here: http://filezilla-project.org/ and install it.
Open FileZilla, you will see a window like this
Fill in your FTP credentials like shown in the image below
now click on "Quickconnect". FileZilla will load your website files, it will look like this:
Navigate to your themes folder. In this case it will be public_html/wp-content/themes/. Not all web hosting have public_html, it may be different in your server. To navigate to the folder themes/ use the right side panel.
When you are in your themes/ folder, using the left side panel, navigate where you extracted the theme folder. For example, i have it on my desktop.
Drag the folder in your web hosting.
It may ask to overwrite files and/or folder. Tick the option to "Always use this action" and click on "Ok" and wait that all files are uploaded.
IMPORTANT: This method will overwrite all your custom code. If you edited some files, your changes will be lost. If this is your case, do not follow the last step of dropping the entire folder and follow the steps below.
The most important thing is to have a list of files with the custom codes.
For example. I edited functions.php and custom.css adding some code.
Open the changelog of the theme, it is in yourthemefolder/Changelog.txt. Everytime we create a new update, we will insert in that file what we changed and which files has been changed. Check the file list and be sure that your custom files are not changed in this update.
For example, you can find a list like this:
As you can see, the files functions.php and custom.css are not changed. I can also not upload them. Open your FTP client and connect to your website. Navigate to wp-content/themes/ and open your theme folder, in this example wp-content/themes/bazar/.
Select all files and folders, except the 2 with custom codes. Drag them and drop all in the right side panel, like in the screenshot below.
FileZilla will ask if you want to overwrite files and folders. Say yes and overwrite all files and folder.
If your custom files are in the UPDATED list, you have to update them manually. You need to add your custom code in the updated file again and only then upload it overwriting the file online.