ON YOUR LETTER HIT CTRL + A TO SELECT ALL, THEN HIT CTRL + C TO COPY EVERYTHING

ON THE ABC TEMPLATE USE THE MAGIC WAND TOOL TO SELECT THE RIGHT BOX FOR YOUR LETTER. 

*MAKE SURE THE ABC TEMPLATE LAYER IS SELECTED IN YOUR LAYERS

ON THE TOP BAR HIT EDIT-PASTE SPECIAL-PASTE INTO

PRESS CTRL + T TO RESIZE TO FIT BOX