"Um..."

The dreaded "um"s...

They're placeholders for what you meant to say but forgot, or don't quite have ready yet, or for filling the space left by your brain as it struggles to keep up with your mouth when you're speaking extemporaneously. Usually, its use has become so ingrained that it seems impossible to speak without involuntarily relying on it.

But...there is a cure: PRACTICE!

You need to figure out where you are going with each part of your presentation/speech, then practice its delivery until there's no need for filler. Recording yourself delivering the speech can be a helpful tool for eradicating "um"s as well.

Don't leave room for doubt: be sure.