When even the legendary Le Bernardin is changing things up to remain relevant, all restaurateurs would be wise to consider tweaking things. Two Manhattan restaurants—one, La Mangeoire, a long-time neighborhood eatery, and the other, La Silhouette, a bistro opened in 2011—have managed to adjust to the changing economy and remain profitable, despite not having a celebrity chef or the buzz of a super-trendy hot spot. Here's how they did it.

Offer smaller plates. La Mangeoire, in Manhattan's Upper East Side, offers its main courses in full and half portions, with prices adjusted accordingly: The duck leg confit, served with cranberry beans and tomato stew is $25.50 for the smaller size, $34 for the larger. "Since the smaller portion was introduced, sales have progressively gone up to three-quarters of our main course sales," says owner Gerard Donato. "The actual dollar sales went down in the beginning, but went back up since customers appreciated the new portions and came more frequently."

Consider doing a takeout menu. Sleek and trendy in décor, La Silhouette in New York City's Hell's Kitchen doesn't look like a typical takeout joint. But the owners were enthusiastic about tapping a new market. "Takeout opens a new revenue door that wasn't there before," says Sally Chironis, who co-owns the restaurant with Tito Rahman. "We know a lot of businesspeople who don't have time to go out to dinner or lunch and we felt strongly that we would be filling a niche for those diners—and they are anything but downmarket. The response has been overwhelming and we have already established some corporate accounts."

• Revamp your space. "I have owned and operated La Mangoire for 30 years and the space was in need of a facelift," says Donato. This involved a new paint job and incorporating reclaimed barn wood, burlap tablecloths, and new soft lighting fixtures into the décor for a fresh "Country Rustic" look. "We spent several thousand dollars to make these changes," says Donato. "I view these changes as a medium-to-long-term investment—not an immediate increase for our bottom line, but an increase over time."

Expand your menu—but don't forget about your regulars. Donato and chef Christian Delouvrier expanded Le Mangeoire's restaurant concept beyond its previous Provencal bent to an overall feeling of French country cooking, but made sure to keep popular dishes on the menu. "We still serve our Calamari grilled a la plancha and Endive and Roquefort cheese salad," says Donato. "Our customers welcomed the menu changes with open arms, but when regulars started asking for these dishes on our comment cards, we knew they had to remain. We are counting on the menu changes to attract the attention of the press, which we hope will increase reservations."