What tool should I purchase in order to replace the bottom bracket in my Giant Defy 3? I'm changing my front crankset from Gossamer FSA 105 to Shimano 105 FC-R7000 in my Giant Defy 3 road bike from 2015... 

I kinda stuck on removing the bottom bracket as I'm not sure which type of tool should be used for that sort of job... Could anyone point me to the right tool for removing the bottom bracket? Please see attached photo of my bottom bracket. Thanks in advance!
You don't need to remove or replace the bottom bracket to fit R7000 series 105 cranks (unless the bearings are won out of course). The Shimano SM BB72 bearings are Hollowtech II for a 24mm spindle so the R7000 will fit.

If you need to replace the bearings, special tools are needed to drive the press fit cups out of the bottom bracket shell and press new ones in. This must be done properly - the cups have to be driven out and pressed in square to the shell otherwise it can be damaged.

The tools are relatively expensive so it's a good idea to get a local bike repair shop to remove and press the bearings for you.