you can boot from the USB Live Medium and when there is partitioning during install you can remove all old partitions. (Reclaim additional space). I always used automatical partitioning afterwards.
Automatically configure partitioning -
If this option is selected, then after
you press Done in the top left corner
of the screen, the installer will
determine the total amount of space on
all selected disks, and it will create
a Logical Volume Management (LVM)
layout suitable for your system. The
specifics of this layout depend on
whether your system uses BIOS or UEFI
firmware, the total amount of free
space on your disks, and the amount of
RAM on your system (which determines
the size of your swap space). With
automatic partitioning, you can also
select the I would like to make
additional space available option
below. Use this option if you want to
reclaim space from an existing
partitioning layout - for example, if
a disk you want to use already
contains a different operating system,
and you want to make this system's
partitions smaller to allow more room
for Fedora. The Reclaim space dialog
which opens if this option is selected
is described later in this section.
..
If you selected automatic
partitioning and the I would like to
make additional space available, or if
there is not enough free space on your
selected hard drives to install
Fedora, the Reclaim Space dialog will
appear. This dialog lists all disk
devices you have configured and all
partitions on those devices. The
bottom right corner of the dialog
displays information about how much
space the system needs for at least a
minimal installation and how much
space you have reclaimed. Warning If
you use the Reclaim Space dialog to
delete a partition, all data on that
partition will be lost. If you want to
preserve your data, use the Shrink
option, not the Delete option. First,
review the displayed list of available
storage devices. The Reclaimable Space
column shows how much space can be
reclaimed from each entry. To reclaim
space, select a disk or partition, and
press either the Delete button to
delete that partition (or all
partitions on a selected disk), or
Shrink to use free space on a
partition while preserving existing
data. Alternatively, you can press
Delete all in the bottom right corner;
this will delete all existing
partitions on all disks and make this
space available to Fedora, but all
existing data on all disks will be
lost. After you free enough space for
your Fedora installation, press
Reclaim space to finish.
(see https://docs.fedoraproject.org/en-US/Fedora/25/html/Installation_Guide/sect-installation-gui-storage-partitioning.html
Can you write lsblk in a terminal, and post the output here?
Yes :) I edited my question :)