You're toilet isn't too difficult to remove,
only two bolts attache it to the flange. My flange screws in to the tank but some might be glued. You don't have to remove the flange to change the toilet.
One bolt is accessed through a round plug that's visible once you lift the seat up. The other is either at the back or under the foot pedal.
You may be able to repair or replace the flush valve or you can get a replacement.
Make sure you get a new toilet the correct height!
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