A Mezuzah must be placed in the upper third of the doorpost, irrespective of the height of the door. If a person recited the blessing and placed it below the top third, and later realized, or was made aware of the error, he has to remove it and reposition it in the top third.
In such a case, he should not recite the blessing again when moving it. One of the reasons is that there is an opinion that if it is placed below the top third it is still valid. And even though we do not follow that opinion, since there is a difference of opinion we apply the concept of Sefeq Berakhoth Lehaqqel (when there is a doubt whether a blessing should be recited or not, we do not recite it).
Therefore, in this case of moving the Mezuzah to a higher spot on the doorpost, it should be repositioned without a blessing.
(See Ben Ish Hai, Shanah Beh, Parashath Ki Thabo, Oth Heth)
