how to reduce used capacity in data protection?

A customer of ours uses vSphere Data Protection.

In the reports, I see that Used Capacity is growing at 1%~2% per day.

It has reached 86.31%.

We removed old backup some days ago, so it should have been able to complete the maintenance, but it is still growing.

How can we lower the used capacity?

Thank You very much and regards

Rodolfo Giovanninetti