Cowell confirmed the shake-up during a lengthy Twitter session on Monday night, in which he discussed both his shows and his personal life.
He tweeted: "There will be a lot of changes on X factor UK and USA. But good changes. I feel excited for both shows this year."
Cowell didn't confirm whether the changes included the judges, following speculation about who will be returning to the panel.
It is thought Gary Barlow, Nicole Scherzinger and Louis Walsh will be back but Sharon Osbourne has been tipped as a possible replacement for Tulisa Contostavlos.
However, Tulisa has denied umours she has been axed from the show.
Simon's series of messages started when he apologised for not tweeting more often.
He went on to give updates on various projects, including music acts he signed following The X Factor and The X Factor USA.
He said he had "a very good feeling about" X Factor winner James Arthur and fellow contestant Ella Henderson.
He also offered his opinion on the One Direction movie, saying early footage was "very exciting".
He said the bandmates "continue to amaze me", describing them as "hard workers but still the nicest guys you could hope to work with".
Towards the end of his online session Simon showed his softer side, writing: "And with everything I have been working on it made me realise that your friends and family are still the most important things in your life."
He went on: "Sorry to cram all this in. Have read some strange things about me recently. I am happy. Healthy. And enjoying life. Hope you are too."
He later conceded that he had been "a little deep", but explained: "It was one of those nights you realise you have a lot to be thankful for."