There have been periodic suggestions from members that the logo or name or both should be changed but they've never gained any traction. It seems that the decision has been made by a committee (presumably of the NEC) to change the logo and shorten the name officially from United Kingdom Independence Party to UKIP - a change that most people made years ago.
The name change makes sense because the party is almost universally known as UKIP but the £ sign logo is instantly recognisable as UKIP. The Tories changed their logo in 2006 from the torch to the much-mocked tree yet the torch logo is still recognisable and in fact a Google image search for the Conservative logo will bring back many copies of the torch logo on the first page while many of the tree logos shown are parodies.
UKIP is now accepted as a credible political force with a growing support base and a fatal challenge to the established two and a half party establishment. Changing the most recognisable thing a political party has - its logo - when it has finally broken into the mainstream just doesn't make sense. If it ain't broke, don't fix it.
There is a straw poll for members on the UKIP Faculty group on Facebook on whether the change of name and logo is welcome.