This is from memory, and I haven't done it in over a year, but here goes (and subsequent posters may correct):
[1] Transfer the file to your 48 (I can't advise 49, but strongly suspect it's the same procedure).
[2] Locate to the directory of your choice (the attachment is to a directory, as I've always done mine to HOME, they're always visible everywhere, but I inferred that attachment to a subdir would conceal...).
[3] Recall LIB to the stack (may or may not then PURGE original name).
[4] STOre to the PORT; for 48S & G, use "0 STO" (that's numeric zero then STO), others may have more PORTs to play with.
[5] Turn the 48 off, then on. YOu should see a delay in it coming back on, and you'll be in HOME.
[6] Check the LIBrary to see that it's present, and test as appropriate.
I look forward to corrections....