Does the approach controller tell you when to contact the tower controller?

Approach Control or ARTCC will always switch you to tower control before you enter Tower’s airspace. This applies whether you are flying VFR or IFR

You cannot change frequencies without permission except in the case of lost communications. There MUST be a positive handoff of ATC control.

Most common way is approach control telling you...

"Clipper 123, contact tower 118 decimal zero" -

Or, you ask...

"Kennedy approach - Clipper 123 has runway in sight!" -

or

"Clipper 123 is 1 mile final, confirm cleared to land" -

It has happened that we got cleared to land by approach control -

They might say "Clipper 123 cleared to land, contact tower after landing 123 decimal 4" -

.

He'll usually tell you, but sometime they forget.