all sounds can be changed in the composer, just go to the pattern, select a track and change the sound by selecting it, then exit out.
there are various programs to recover deleted files, assuming they are not simply in the recycle bin. However if you use the computer you risk overwriting the deleted files since they have been marked as free space, and windows may use that space as swap file area and other functions, in that case the data will be lost and corrupted. Therefore you must run a file recovery program as soon as possible to stand a chance of success.