You might have to root your phone first.., there are a lot of threads here which will guide u to root your phone.
But personally i find flashing the pre-rooted rom (http://forum.xda-developers.com/q101...one-d-t2883342) provided by "Reconfigured" using the sp tool is simple method. ( please say thanks to him )
then you can install the Font installer app from the play store to install the font you like.
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