Adjusting a FD is REALLY simple! Granted, you can probably get the LBS to fix it for free, but if you want to know how to dial it in yourself, read on.
There are two ways to adjust a FD. There are two small screws called 'limit screws' on the top of the derailleur. They control how far the FD swings in each direction. The FD rocks inward until it hits the "LOW" limit screw and it rocks outward until it hits the "HIGH" limit screw. You want the chain to be centered in the FD cage, and parallel with the cage when the FD is at each of the 3 (or 2) chainrings on the crank. Those limit screws adjust the maximum travel of the FD in each direction. Use a screwdriver, and turn one while you watch the derailleur. You'll slowly see it travel in one direction. If you look closely at the FD, it should become clear how it works. After you're done playing, put the limit screws back where they were when you started. If you simply had a cable replaced, it's unlikely that the shop moved them.
The other way to adjust a FD is by varying the tension of the shift cable. The cable pulls on the FD when you move the shifter to shift to a larger chainring, you're pulling on the cable, and pulling against a strong spring in the derailleur. When you want to shift back down to a smaller chainring, you're releasing an amount of cable, and the spring pulls it back and allows the FD to move. If there is not enough cable tension, when you go to shift upwards to a larger chainring, there simply isn't enough travel to get the FD into a position where the chain will grab that larger ring. If there is too much cable tension, the FD will tend to not shift down to a smaller ring easily. This is because the spring in the FD must swing from it's own internal spring. Too much cable tension works against that spring, and doesn't allow the FD to swing fully.
It sounds to me like you don't have enough cable tension in your FD shift cable. There are usually a couple of simple ways to fix this.
1. Follow the FD shift cable along the frame. You should see a boss brazed onto the frame somewhere with a 'barrel adjuster' on it. This adjuster can be screwed in and out. By screwing it out, you're essentially pulling on the cable and increasing the tension.
2. Sometimes, depending on your bike, you may have a similar adjuster near the shift lever. Again, backing out this adjuster ends up pulling on the cable making it tighter.
3. Lastly, you could also loosen the screw that clamps the cable in the FD. Loosen this screw, pull the cable tight, then retighten the screw. This is more of a pain in the butt because it's tough to make precise tension adjustments this way. Option 1 is your best bet.
Put your bike on some kind of stand to get the back tire off the ground. If you don't have a stand, ut it on a crate, hang it from the rafters, whatever. Try adding some cable tension, a little at a time, and spin the back wheel. While pedaling the back wheel, try to shift up and down the front chainrings. This is usually an iterative process of adding some tension, checking the shifting, adding tension, checking, adding, checking, letting some tension out, checking... you get the idea.
I've found that these tasks go much smoother with some type of radio playing in the background, and a cold beer close by.