Dentures will affect your speech, especially in the beginning. It will take a few days to have your ears retrain your mouth on how to pronounce words again, especially SH, F, and TH sounds.
Quite often patients will have lost their natural teeth over a period of years, so gradually, they train themselves to speak with the missing teeth. When you get new dentures, in an instant, your mouth is full of 28 teeth again. This can be a challenge, but it is always overcome. It just takes a bit of time, and practice.
The best solution is to read aloud, (usually at home), to allow your ears to train your tongue on where to re position itself to create the sounds clearly again. This will come naturally, and it will be second nature after a few days.