The semimetallic, two-dimensional layered transition metal dichalcogenide WTe2 has raised considerable interest due to its huge, non-saturating magnetoresistance. While for the origin of this effect, a close-toideal balance of electrons and holes has been put forward, the carrier concentration dependence of the magnetoresistance remains to be clarified. Here, we present a detailed study of the magnetotransport behaviour of ultrathin, mechanically exfoliated WTe2 sheets as a function of electrostatic back gating. The carrier concentration and mobility, determined using the two band model and analysis of the Shubnikovde Haas oscillations, indicate enhanced surface scattering for the thinnest sheets. By the back gate action, the magnetoresistance could be tuned by up to similar to 100% for a similar to 13 nm-thick WTe2 sheet.