Sauber hope they will be more competitive after an "extensive weight reduction" since the last race in China.
Head of track engineering Gian Paolo Dallara told reporters a "significant" aerodynamic update included a modified wing, engine cover and side pod fins and deflectors.
He added: "We will also have a software improvement which will enable us to use the potential of the power unit in a better way."
A season's best result of 11th, coupled with three retirements for Adrian Sutil and two for Esteban Gutierrez have left the Ferrari powered team joint bottom of the Constructors' table, with Lotus, Marussia and Caterham.
With the resurgence of their recent rivals Force India and Williams, Sauber are in danger of falling away from the midfield pack.
Dallara also said ahead of the Spanish Grand Prix: "Making the best use of the tyre compounds will also be a challenge, as Pirelli's choice to allocate medium and hard tyres appears to be conservative.
"We very much look forward to converting everyones' efforts into improved lap times."
"We know that all the other teams are progressing as well, so it will be interesting to see where we stand. We will certainly do our best in order to race for points."
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