Do you mean you want to reduce echo that is in a recording you have already made? If so, you can have a look at these plugins that can be of help:
These both run as plugins so will need to be hosted in a DAW software (or audio editor that features plugin support). A DAW can also be a solution for editing your audio.
Many, many upcoming filmmakers overlook the importance of audio. If it is something that really interests you, then why not take on the challenge of editing and mixing. But you should be aware that there is a lot of skill involved and it's not something that can be learned overnight.
The best is to have the cleanest possible audio to work with in the first place. However, if you do have poorly recorded dialogue you may also need to consider re-recording the dialogue (ADR).
As for which software to use, just type "audio editor" or "DAW" in the search field of this site and you'll find plenty of useful tips.