I made it through the GUI this time, not using the command line:

• Opened Gnome File Roller (Applications ->Accessories->Archive Manager)
• Dragged the folder I wanted to compress inside it
• Click “Create Archive”
• Click “Other Options”
• Tick “Split in volumes of” and choose the split size (how many MB you want each file split to be)
• Choose “Archive Type” to be “7z”. Note: I selected “Automatic” at first, but it didn’t work! Do you know why??
• Click “Create”
• Enjoy 🙂