movies in photo

My startup disk is full on my desktop. The reason is a large amount of movies. For convenience working from my lap top I moved all the movies to 3 flash drives. I am checking to make sure each movie is indeed on the flash drive, (one by one) and then deleting the movie on the lap top. I have deleted more than half of the 1300 movies that were originally in that file. I thought as I did this the movies would also be deleted from my desk top. In checking yesterday, they are not. I still have all of those movies on my desk top. Not sure if I understand how this all works. When I take a movie it automatically goes to both places. If the movies are not in sync I will have to go thru same process with my desk top. Any suggestions. Thanks for any information or ideas.