"joya" usually translates to "jewel"
"joyas" (plural) usually translates to "jewelry"
"joyería" is the store where they sell jewelry, and it can also be where they design them, "joyería" can also refer to the act of designing and producing jewelry.
So, to answer your question, the phrase you wrote would say:
" Antes de venir al hospital para la operación, póngase ropa cómoda y deje las (sus) joyas en casa."
Espero que esto te lo aclare un poco más. Suerte!