There are a couple ways you can do this. You can upload that file using your local FTP software or you can upload that file using the upload file feature built into the DESIGN > MANAGER admin tool.

If you use the FTP method make sure you upload your file to the proper template set. You'll find all template sets usable within your site within the /geo_templates directory on your site. Once your looking at the contents of the geo_templates directory you'll see a /_temp, /default and any number of other directories. Leave the _temp directory and the default directories alone. The first is an internally used directory while the default directory contains your full default template set. DO NOT MAKE CHANGES IN THE /default DIRECTORY. Any changes you make there will be overwritten by a version update. All other directories you see in the geo_templates directory are customizable/customized template sets used in your Geo installation. The names of those other directories appear in the DESIGN > TEMPLATE SETS admin tool. The /default template set will also if you are in advanced mode.

So to FTP a file to a template set choose the corresponding directory name from the ones you see in the geo_templates directory. Any directories you see in a template set correspond to a directory you see in that template set within the DESIGN > MANAGER admin tool. Choose your intended directory and upload.

The software pre-compiles your templates into php files to faster load when called in a page load. The software creates those pre-compiled php files after every change to a template in your template set. But as the software does not monitor "system file change times constantly" it does not know when you have made a change to a template if you upload through ftp directly to the file set outside the Geo software. So as the software does not know you've changed a template it cannot pre-compile that template. The client side pages are "built" from these pre-compiled php files and NOT directly from your templates. So if you upload files through ftp you need to tell the software there has been a template change and to recreate all pre-compiled templates. Click the "rescan attachments" button next to the template set you just uploaded to so those background processes can take place:

DESIGN > TEMPLATE SETS

That will force the software to recompile templates so you can see your just uploaded changes on the client side.

The DESIGN > MANAGER admin tool contains within it a convenient upload file tool. You can use that to easily include files in your template sets. To do so navigate to the directory you want to include/upload the file into within the DESIGN > MANAGER admin tool and click the upload file button in the top right of that tool. A popup will appear that will allow you to choose a file from your local computer. Choose the file you want to upload and click the upload button. That file will be uploaded to the location and filename you choose.

Do not change the file type within the upload file popup. Leave the file type (.jpg, .gif,…etc) the same and change the filename to what you want. Changing the file type will only confuse the browser downloading it and trying to display it. The filename will say one thing while the headers in the file same something different. Most browsers can overcome the mistake but there's no use leaving that to chance.

The specific "file upload" feature is here in the DESIGN > MANAGER:

Once you upload an image into your template set it will be "portable" with the rest of the template set if you decide to get a backup or move to another GeoCore installation.

If you were to upload an image (for example: image.jpg) into the following template directory:

/external/images/

You could then use that image within any template of your template set using the following tag:

{external file='images/image.jpg'}

If you wanted to use that in an html image tag that code would look something like:

<img src="{external file='images/image.jpg'}" alt="uploaded image" title="uploaded image">

Of course the image name (image.jpg in the above example) would be your image files name instead.