gpt disk partitioning is recommended on a machine new enough to use it. To change from dos partitioning to gpt, run a disk partitioning tool like gdisk, delete all the current partitions, create a new partition table as gpt, then remake partitions in the size you want them. Google for recommended partitioning schemes -- search for disk partitioning recommendation for ubuntu . These days, a swap partition is not necessary and is not automatically created because a swap file is used. Fine, unless you want to have multiple installations on the disk and have them share swap. I like to have two partitions for root, so I can try out a new release without giving up the current one being used. Make a swap partition if you will eventually have multiple installations. I like a big data partition, mounted at /usr/local/data. Not /home, because with multiple installations, the home directory has release specific files. From the any release's home directory, you may add links to the data partition as needed. Make a 300M partition first, for the EFI partition.
At the installer, chose the "something else", select the partitions you created, and set what they contain and what they are to be used for (e.g. fat filesystem, efi or ext4 filesystem, root).
The mode (UEFI vs legacy) the installer is booted determines the way the install is done.