The toilet flush is easy to replace in most cases. Whether you want to change the handle to match the decor or the old handle has broken, replacement can be done in fewer than five minutes.
Remove the toilet tank top and set it safely aside. Inside the tank you will see the handle, a nut securing it in place and the linkage to the flush valve's flapper at the bottom of the tank. Disconnect the chain or whatever links the flush handle to the flapper. Hold the flush handle and use your fingers to loosen the nut securing the handle. If it won't loosen, use a pair pliers to loosen the nut. Remove the nut and pull the handle from the outside through the opening.
Install the new handle's lever through the opening and position the handle to its desired permanent position. Slide the nut over the lever inside the tank and up the handle's threaded connection. Finger tighten the nut, it shouldn't be necessary to use a tool.
Reconnect the linkage from the flapper to the flush lever. There should be a small amount of slack in the linkage but not so much that the slack can get under the flapper and prevent a proper seal.
Test the flush handle and watch the refill cycle to make sure everything is working properly. If it works properly, replace the tank lid and you are done.