Don't do it. You have several advantages with friction shifting, not the least of which is almost all drivetrain parts will work with it, where index systems require a dedicated system-- not only will you need new shifters, but new mechs, new chain, new cassette/freewheel. You can trim shifting with friction. Many index systems develop problems where they need to re-adjusted to shift properly; in practice, not hard, but a PITA when a problem develops in the midst of a ride. If you're used to friction, keep it.

The shop is likely going to charge you beaucoup l'argent. You want a shifting up grade, get some simplex retrofriction shifters, about forty bucks on ebay.

Note: re-edited after my overworked and underpaid editor, USAZorro, noticed a number of major Faux Pas. Oops! Thank, Z!