If you still have the CD there is a procedure to join the CD tracks as you import it into iTunes.
Put the CD into your CD drive and when it shows up in the iTunes Import CD window:
- make sure that it is in track order (which it should be as that's the default setting)
- select the first track, the Shift/select the last track. All the tracks should now be highlighted in blue:
- in the screenshot below, tracks 1 & 2 have been joined, tracks 4, 5, 6 & 7 have been joined while tracks 10, 11 & 12 are selected, waiting to be joined (as you can see once the gear wheel (to the right of the Import CD button) is selected:

- click the Join CD Tracks option and the tracks you have selected will show as joined (i.e. tracks 1 & 2 in the screenshot)
- You may need to rename the CD in order to keep it separate from the original import. Either:
- name the new copy as <same CD Title>2
- delete the old copy of the CD (not always the wisest move until you are certain the the re-import is successful)
Note:
- you can only join adjacent tracks
- you cannot join tracks unless the CD is in the correct track order, as shown by the arrow at the top of the number column
- the option does not show up unless you have selected tracks
- if the Join CD Tracks option is not shown, it means that the selection is not valid:

iTunes is not able to join the tracks once the album has been imported, so if you no longer have the CD, or you purchased the album as a digital copy, you will have to use a third-party audio editor, such as Audacity to combine the tracks. However, although Audacity is free to use, it does have a steep learning curve in order to achieve what you want. In addition you will need to add the revised album into your iTunes Library (a procedure that is fairly easy).