If so, have you tried holding down Alt while holding the left mouse button and moving the window around with the pointer?
Unfortunately, this doesn't work with flwm.
You can try these key combinations:
Ctrl Alt arrows moves the window
Ctrl Alt = grows the window (unshifted + key)
Ctrl Alt - shrinks the window
Ctrl Alt PgUp grows the window veritcally
Ctrl Alt PgDn shrinks the window vertically
Ctrl Alt , grows the window hortizontally (unshifted < key)
Ctrl Alt . grows the window hortizontally (unshifted > key)
Ctrl Alt t taller (sames as PgUp)
Ctrl Alt s shorter (same as PgDn)
Ctrl Alt m maximize widow
Ctrl Alt v maximize vertical
Ctrl Alt h maximize hortizontal