Replace is to replace any string with any other string. You can replace all occurrences of that string or specific occurrences. You can also use case sensitive option to replace case sensitive string only.
Remove the specific string. It has same option as replace like removing case sensitive string or all or some occurrences of that string.
Remove character used to remove unwanted characters from the file name.
This is how it should be used. Like you wanted to remove characters @, %, ( , ! and & from the file name.
All you have to give is @%(!& in 'This' Field. Application will remove all occurrences of @, %, ( , ! and & from the file name.
So basic difference between Remove and Remove character is that in Remove it uses whole string to find from the file name and remove it but in 'Remove character' it finds each character from the file name and remove all of them. This is great to remove unwanted characters from the file name in a single operation.