HELP: Regex pattern matching

I have an ASCII file which has multiple blocks of text I want to clear. The
scheme is as follows:

=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-
line 1 Everything between the separators,
line 2 including the separators
line 3 I want to clear from the text file
line 4
-----------------------------------------------------

This text I want to keep

There are infinite number of blocks surrounded by exactly the same
separators.
So, I guess I need to clear everything between the starting "=" and the
ending "-".

Can anyone suggest a regex pattern string that would help me accomplish
that?

Thank you all guys in advance!

Nasko