If you are doing a new install you don't need to delete any files. The installer will give you the option to delete partitions when choosing where to install, simply delete all the existing partions. Once the installer has created new partions none of the old files will be visible. Technically some of the data is still recoverable (by reading the raw device), but in normal use it has gone.
If you really want to delete stuff on an SSD then "secure erase" is probably the way to go. Booting into the UEFI BIOS may well provide a "secure erase" function. You only need this if you have some security reason for erasing the data, simply deleting the partions is likely to be sufficient in most cases.
