roof tile?

I take it you mean concrete interlocking tiles and not the flat concrete tiles.

Cut 3 3inch x 2 or similar blocks, A bricking trowel to leaver up the tile/s. AND WORK GLOVES.
shove the trowel under the tile you want to lift work it up and the tile next to it will also rise. block that one so it doesn't drop and the one above the tile you want to remove. That will take the weight off the tile you want to remove then work that tile out of the gap.
To replace you may need to adjust the blocks position to give extra room.

Flat tiles you will find are nailed every fourth or fifth row. so if you haven't a slate/tile nail rippper lift up the one above slide them up to clear tile your removing and prise up the nailed tile. Fit the new and don't forget to tack that down with galvanized nail/s.

Bob
October 2010