hello spagatoni, yes you probably can fit wider tyres, it depends on the width of the rims, but its very likely that you could put 205 section tyres, can i ask why you want 40 profile tyres tho, is this to prevent tyres touching the body, if so then you might find this help full
Specification Sidewall Radius Diameter Circumference Revs/Mile
195/45-15 3.5in 11.0in 21.9in 68.8in 921
205/40-15 3.2in 10.7in 21.5in 67.4in 940
215/40-15 3.4in 10.9in 21.8in 68.4in 926