windows 7 Change from Spanish to English

No, you must remove the Spanish version first so that the partition is empty.
(Windows Setup must have an empty partition to install to).

Boot your PC from the Windows 7 English disc and format the existing Windows partition.
Then select that partition for the new Windows installation.

Or you could just delete the existing Windows partition and create new parttion.
Then choose that "unallocated space" for the new installation..
Windows Setup will automatically format it first.