Everybody’s Opinion Matters

It has often been said that you will catch more flies with honey than with vinegar, and though it's a little crude, the fundamental truth of it when pertaining to your coworkers is also true.  People want to feel needed, however what’s more is that they love to feel as though their viewpoint counts.  And if you are intending to make any type of change to a procedure or any kind of change to a process that has been going on the same way for a long time, then it pays to ask the opinions and for the help of the people involved. 
This includes the individuals that are using the process at the moment as well as individuals that came up with the process in the first place.  Yes, you are trying to correct or tune something that somebody has already put a lot of work into, so you do have to do it in a cautious and respectable manner.  That is to say you need to use some courtesy and some common sense in the way you approach them. 
If you simply come right out and tell them what is wrong and why their process is so bad, they may not be willing to help you make the changes or give you the insight that you're looking for.  Maybe there is a reason that is tough to see or hard to explain and that's why one choice was made over another.  It would be nice to have these views and insights in advance, before changes are made and a process is modified beyond repair.  
You're looking to streamline a process, to make it function better, so it might be helpful to get the reasoning behind why it is the way it is now.  Then, with a new set of eyes and some different perspectives, you may have a better chance at coming up with something new that works better.  Once again, forcing the issue and being disrespectful may not help you achieve the goals that you're looking for.  
With a little bit of consideration and tact, you will be able to gain a helpful hand in beginning the project and you may have more willing participants.  The more willing the people are involved in adopting the changes and making them their own, the better chance you'll have in seeing the alterations take hold permanently and do real well.