I have an All-in-6 dental implant and got permanent teeth but I am not happy. I have speech problems.

It sounds like what you have is a temporary fixed prosthesis. It's important to make notes of all of these issue as these could probably be corrected in the design of the final prosthesis. It is normal, especially in the beginning, to have difficulty with your speech but even with the temporary prosthesis you should adapt after a few months. Every case is different and I am not familiar with your exact situation, so please address your concerns with your dentist. 

The All-on-4 is a wonderful treatment, however, there can be an adjustment process during which your tongue will once again learn to pronounce certain sounds such as when you make the "sh" and "sss" sounds. This is normal and most patients are able to adapt fairly quickly. You will also be learning to eat and chew with your new set of teeth. As long as the prosthesis is adapted to your gums properly, you should begin to see improvement over the next few weeks. 

I am sorry that you are having so much trouble with your speech.  It could very well be that you are still in your temporary screw retained prosthesis.  The temporary's are always made a little bulkier due to the fact that the temporaries do not have the titanium bar (like the finals) it can take a patient 1 to 2 months to get used to the temporary teeth.   When you proceed to your final permanent teeth this will be corrected with the design.  

Sorry you are having such problems with your implant supported denture. It sounds like the positioning of the teeth may be the problem. With the all on 4 dentures you do sometimes get spaces underneath the denture and gum. This can lead to speech and leakage of air which does affect the speech. It is hard to make a judgement on your case since there are so many variables that can affect you. You may want to get a second opinion. Hope this helps.