(This is a duplicate picture from the previous screen.)
Now click on the 'look in' box, and browse to the folder with your pics. Click on the 'Add all' button, and you will now see the pics listed on the left.
Now click on the Batch rename button, and then the 'set rename options' button.
You will now see a screen like this;
Now fill in the name you want to give the pictures, as you see here, I have used a where/when name, and put the '#' sign after, which means they will be given consecutive numbers. If you use the '$' sign, it will put the old name on the end. Click on 'rename input files', and then 'overwrite existing files'. Now click go, and you will return to the 'Batch conversion' box. Click 'Start', sit back, and smile.