You may be able to prise the nail free by lifting the bottom edge then again it might snap the tile so have a spare handy.
How to remove bottom row of roof tiles.
If they are all nailed then its a bit harder.
Generally it is not necessary nor desirable to nail every single tile on roofs nailing as described here will provide a fully functional roof while allowing individual tiles to be remove later if necessary.
Position the first roll of underlayment at one side of the roof perpendicular to the lower edge the eave of the roof.
Do this using two pieces of timber to hold them up.
This will expose the nail on the tile on the bottom row.
If your tiles aren t lifting they may have nails holding them in place.
Working with roof tiles is a lot easier when you know a couple of basic tricks.
They are not hard to remove either the hardest part being lifting the first tile.
You may find that you need to go up a couple of rows to find an un nailed one then then work back down.
This will lift the overlapping tiles on the row above so the tile you want to remove should come out easily.
Some of the tiles may have clips or nails holding them but not all.
Removing a tile from the roof.
As you roll out the underlay keep the bottom edge of the material aligned with the edge of the eave but above any metal or synthetic edging that may cover the borders of the eave.
You simply slightly lift the tile at the rear of the one you want to move and then lift the front and slide back the lower tile.
Once you have safely gotten to the broken tile you ll need to slightly lift the tiles that overlap the one to be removed.
Every tile of the 2 rows at the eaves both the half and full tiles those up verges and along the 2 rows at the ridge both the half.
How to replace a roof slate.
This video from bunnings shows you how to take a tile off and replace it prop.