Your computer keeps a list of different file types (identified by their file extension, three invisible letters after the period at the end of a filename) and a list of programs that are installed. Each file is set to open with a specific program (called the file association,) but you can change those settings on your own computer:
1) Find a file that is opening in the "wrong" program
2) Right-click and choose "properties"
3) To the right of "Opens with <program name>," click "choose"
4) Select the program you want to open that type of file (the computer should list any installed programs capable of opening that type.) then click "OK"