In practice,  changes to a bill as recommended by the senate can be accepted, modified or rejected by the house and it has done all 3 over the years.

Also in practice, if the senate votes against a government bill then the house can try to reach a compromise in the bill that satisfies both parties and send the amended bill back to the senate for approval.  

But the house also is empowered to ignore the senate's opposition and to resubmit the bill to the upper chamber for final approval and passage.

For many decades, the senate has then speedily approved the bill the second time around.

This is known as The Doctrine of The Second Bite.

It ensures that the elected chamber has the final say as it should.

Most of this is not in the written constitution but rather is well established precedent.

So yes, the senate can delay the passage of bills and try to amend them but the ultimate authority is clearly in the house.