By default, Presenter will automatically upload any media files that you import into the Media Library to your WorshipTools cloud, given that you have a stable Internet connection. However, if you don't want Presenter to do this automatically, you can turn this setting off: Navigate to Settings and scroll down to the bottom of the Cue Defaults page. Under the Media Defaults section, uncheck the box for Upload Media and Save your change.
Once you've done this, media files will not upload to the cloud unless you manually choose to upload each one to the cloud. To do this, go to the Media Library and click on the "i" icon that shows up when you hover over a media file. There, you'll see a line for "Saved in cloud," and it should say "No" with a green Upload button beside it. Click Upload to save the selected file to the cloud, and repeat for any other files you want in the cloud.