upgrade Dynaudio Special 40 to Kef Reference 1

There is no evidence that the kef reference one is perfect or better. 
Kef came out with the LS50 which is much cheaper than ref 1 yet they say the LS50 is one of the best. Every speaker on the market is "the best". There are no bad speakers. its a hoax 

I do think it’s strange that when you go to the Kef website, they list the blades and the LS50 as their flagship lines, and the ref line and everything else under hifi lines. 
At least it was that way up until a few weeks ago haven’t checked recently. 
Does seem odd that they’d sell ref 1 at many times the cost of “flagship” LS50. Odd marketing choice on their part to group things that way. 
Note I’m not comparing ref1 to LS50 myself as I don’t really have an opinion. My point only that kef’s marketing groupings are curious 

The ls50’s are one of the best for it’s size and cost.

C’mon kenjit its not so hard to understand that no two things are created exactly equal.

If one must measure speakers relative to others, ability to deliver flat clean bass down to 20hz in a particular room is a reasonable way to measure. Speakers that can do it well ( along with doing all the rest well) in a larger room are clearly better.

Size matters with speakers. As does quality. Speakers must work hard to deliver full range sound in larger rooms.

Ohm Speakers are a good model of this. Room size mostly determines which model is best, how big, and the cost. In a smaller room a larger more expensive model is not necessarily better in that it will deliver too much bass but otherwise the design and sound is similar.

It’s a most scaleable design.

Use your ears.  Audition the equipment at home if you can.  The only way to know if you are getting what makes you smile.   If you can't audition at home bring your gear to the dealer.  Not as good a comparison but you will here some of the major differences. 

Good luck

Like everyone else on here are saying, it seems you are seeking a change in presentation of music.  What 'big difference' do you want or expect?  Both speakers are musically adept but their presentation will differ.  KEF speakers are known for their presentation of large soundstages but then Dynaudio Special 40's are also known for the same thing, since you are presently using them maybe its not enough? There is no safe quick way of finding out until you have personally audition them preferably playing your own music.   At the end of the day it will be you listening to the chosen system, not any one else.....