The ornamental design for an adjustableshelves, as shown and described.
FIG. 1 is a perspective view of the present design;
FIG. 2 is a front view of the present design;
FIG. 3 is a rear view of the present design;
FIG. 4 is a left side view of the present design;
FIG. 5 is a right side view of the present design;
FIG. 6 is a top view of the present design; and,
FIG. 7 is a bottom view of the present design.
The broken lines showing of structural feature is indeed for the purpose of illustrating non-claimed subject matter and forms no part of the claimed design.