To be able to add or change the images of our main slider, we will have to create a "Web Album", for this we will go to:
Web and Networks → Content for portails and mobile app → Photo Album
If we already have an album previously created and we just want to add or modify photos and we do not know how, look for step 1 below.
In the case that we do not have any album yet, we will click on the "New" button to create our photo album.
The following screen will appear when you click on the button:
In this screen we will choose our center and the name of the album that we want, it is advisable to put an easy name to remember such as "Slider Home" for the Album of the Main Screen.
We choose if we want it public or if we want to show it.
When we already have it created we will see that it appears to us on the screen.
Step 1. Press the edit button 
and we will see the following window:
Here we have the general data that we have filled previously, we can modify them if we want.
Step 2. Select the "Images" button on the left side. In the case that we do not have any image and we want to add some we will leave the next screen, in which we can upload the images we want by clicking on the "Image" button and we already look for in our computer the image or the images that we want to upload.
But in case we already have images we will get this one. In which we can upload more or eliminate some of the ones we already have.
To finish one of the steps just press the button "Update".