How does thickness of convex lens affect focal length?

The focal length of a lens depends on

1. The refractive index of the material

2. Radii of the curvature of the two faces.

The lens maker's formula is

1/f = (mu --1) (1/R1 --1/R2)

mu- the refractive index of the material with which lens is made

R1 and R2 are the radii of curvature of the faces.

f- the focal length of the lens thus formed.

your question needs clear information. As the thickness of the lens of same diameter is increased then radii of curvature would decrease, hence focal length would decrease. But as the diameter gets increased then there comes a chance of maintaining the radii of curvature to be the same. If so, then no change in the focal length. But, if diameter is not increased to the right extent then we cannot be sure about the variation of focal length.