Change File Extension Using C#

I have many file types: pdf, tiff, jpeg, bmp. etc. My question is how can I change file extension? I tried this:

my file= c:/my documents/my images/cars/a.jpg;
string extension = Path.GetExtension(myffile);
myfile.replace(extension,".Jpeg");

No matter what type of file it is, the format I specify must be with the file name. But it does not work. I get file path from browser like c:\..\..\a.jpg, and the file format is a.jpeg. So, when I try to delete it, it gives me an error: Cannot find the file on specified path'. So, I am thinking it has something to do with the file extension that does not match. So, I am trying to convert .jpg to .jpeg and delete the file then.

There is: Path.ChangeExtension method. E.g.:

var result = Path.ChangeExtension(myffile, ".jpg");

In the case if you also want to physically change the extension, you could use File.Move method:

File.Move(myffile, Path.ChangeExtension(myffile, ".jpg"));

You should do a move of the file to rename it. In your example code you are only changing the string, not the file:

myfile= "c:/my documents/my images/cars/a.jpg";
string extension = Path.GetExtension(myffile); 
myfile.replace(extension,".Jpeg");

you are only changing myfile (which is a string). To move the actual file, you should do

FileInfo f = new FileInfo(myfile);
f.MoveTo(Path.ChangeExtension(myfile, ".Jpeg"));

See FileInfo.MoveTo