1. Close Lazarus
2. Rename folder "FPC 3.0.0" to something else
3. Start Lazarus again, it will ask for compiler, fpc source, gdb, etc...Set the new paths to FPC 3.0.2
If you want to run different version of Lazarus/FPC in parallel use fpcdeluxe, the good thing is they won't interfere with each other.
PS: I would wait a few more weeks then switch to Lazarus 1.8. A lot of new features, improvements, bug fixes.