This is most people's first trick & is probably the simplest one there is. But it is used in countless other patterns & by learning one new throw you can learn three new tricks in one go: Juggler's Tennis, the Half Shower & the Reverse Cascade.
As you are happily juggling a Cascade all you have to do is throw a ball over the top (what did you think you were going to do?) of the one before instead of underneath.
Juggle a cascade & look at the way your arms scoop, you catch on the outside & throw on the inside. This is known as inside scoop. To make an over the top throw you have to use an outside scoop. Take one ball & practise throwing it from hand to hand, catching it on the inside, scooping & throwing it from the outside.
When you are familiar with the new throw, just juggle, pick a ball & throw one over the top. It may help to use a ball that is a different colour to the rest, so you don't have to put any thought into it which may make you drop. Your over the top throw will have to go a little higher than the normal cascade throws, to just above your head, to avoid a collision. It should also go a little wider as well before being caught on the outside of your pattern. Then just do an inside scoop to resume the cascade.
Practise this on both sides (it is only acceptable to learn things on one side only when you get up to four in one hand standard!), do three from the right, then three from the left, then make every fifth throw an over the top. When you can do that move on to Juggler's Tennis.