Bono makes up the lyrics to most of U2's songs.

The Irish rock band's frontman has confessed that when he's on stage he changes the words to their biggest hits as he goes along as he's become more ''literate'' in recent times.

According to the Daily Star newspaper, he spilled: ''I've been making s*** up on the microphone since we were 17.

''Sometimes it turns into words, sometimes it's just like sound paintings. I've only got semi-literate recently.''

Quoting the Little Richard song 'Tutti Frutti', he added: ''There's an age-old tradition, 'A-womp bam boom'. Sound is everything.''

The 56-year-old rocker also said that he will be switching up the lyrics to their hits during their celebratory tour of their 1987 album 'The Joshua Tree', which turns 30 this summer.

Bono - who is joined by The Edge, Adam Clayton, and Larry Mullen Jr. in the group - said: ''I change the lyrics all the time.

''Not just because I don't remember the original ones, but because I felt the first ones were just sketches a lot of the time. So I do change them.''

U2 recently said that they are hoping to premiere ''one or two songs'' from their upcoming album, 'Songs of Experience' if they feel they ''work well'' with the rest of the set list.

Bassist Adam, 57, previously said: ''It would be very much my wish that we could play something from 'Experience' as part of the show, maybe one or two songs.

''Again, I caution that by saying we really have to see the arc of this show and we have to figure out whether those 'Experience' songs would work well in a stadium in this context, but I'd love to see some of that material out there and people being familiar with it before the album comes out.''

As for when the record, the follow-up to 2014's 'Songs of Innocence', will be released, Adam said they want it to be ''polished off'' first, but it should drop later this year.

He added: ''We all very much feel like it needs to be the end of this year. It's not on any schedule anywhere, anything like that. We're going to get back to that later this year and polish it off and finish it off a bit more. But we think we're there with it.''