There are two ways in which you can do this:
This works as a 'pause' function. You can make edits to the membership if needed and restart it at any time. When members are moved over to your cancelled member list, they are removed from your active member count. You can also choose to cancel the member for a future date so you can set it and forget it.
If you don't normally offer a free plan you can create one under Setup » plans and tick the 'hidden' checkbox so that it does not show up publicly. Move the member over to the new, free plan by going to the member profile » plan » change plan » select the free plan » choose the plan change date as the cancellation date.
When members are moved over to a free plan, they are removed from your active member count. If the member decides to return, you can change their plan back to a normal plan.