When adding pictures, videos or other media to a WordPress Multisite, you may often stumble upon a 1MB limit for maximum upload file size. As a result, if the size of the file you try to upload is bigger than 1 MB, the upload will not be successful.
To increase that limit you need to access the Settings of the Multisite Network, which is done from My Sites -> Network Admin -> Settings.
On the new page you should scroll down to the Max upload file size option. The default value of this setting is 1 500 KB which equals to approximately 1MB. That is why it is shown as 1 MB when we attempt to upload a new multimedia file. To lift that limit set a new higher value, like 1500000KB (~128MB).
When this is done, this will effectively increase the Maximum Upload Filesize limit for this WordPress Mulitsite Network and all of its sub sites. As a result when you attempt to perform a new upload, you will see the new higher value.