(scuse my english i'm french ^^')

You can play it on guitar with the guitar tuned a half step below standard
 tuning. Or play with barred and so play the chords a semitone below

So, without special tuning and with barred, the chords become:
E5 => Eb5
A5 => Ab5
B5 => Bb5

 E5                 A5         E5
Amazing Grace, how sweet the sound,
                         B5
That saved a wretch like me.
  E5                 A5      E5
I once was lost but now am found,
               B5    E5
Was blind, but now I see.

E5                          A5        E5
T'was Grace that taught my heart to fear.
                      B5
And Grace, my fears relieved.
    E5                 A5       E5
How precious did that Grace appear
           B5      E5
The hour I first believed.

E5                     A5         E5
Through many dangers, toils and snares
               B5
I have already come;
     E5                     A5         E5
'Tis Grace that brought me safe thus far
               B5      E5
and Grace will lead me home.

    E5                 A5       E5
The Lord has promised good to me.
                   B5
His word my hope secures.
   E5                  A5       E5
He will my shield and portion be,
           B5     E5
As long as life endures.

E5                        A5           E5
Yea, when this flesh and heart shall fail,
                      B5
And mortal life shall cease,
  E5                 A5      E5      
I shall possess within the veil,
          B5      E5
A life of joy and peace.

E5                        A5        E5
When we've been here ten thousand years
                      B5
Bright shining as the sun.
E5                     A5          E5
We've no less days to sing God's praise
                B5      E5
Than when we've first begun.