Open the item from your Inventory list, change any field — name, price, condition, category, note, or photos — and tap Save.
Editing an item doesn't change its barcode — the barcode is the item's SKU, which stays the same, so a tag you've already printed will still scan correctly. What it won't update is the price (and name) printed on that tag. So after a price change, reprint the tag so the price the customer sees matches what rings up at the register.
You can edit your own items anytime. A few things are set by the store and can't be changed from your side — your commission rate and the store-wide Sale Mode percentage. For those, check with your store admin.