You need to do a total removal before reinstall the Lazarus/FPC:
01. Uninstall lazarus, fpc, fpc-src
02. Delete ~/.lazarus, except: editoroptions, environmentoptions
03. Delete /etc/fppkg (folder)
04. Delete /etc/fp.*
05. Delete /usr/share/fpcsrc (folder)
06. Delete /usr/lib/fpc (folder)
07. Delete /usr/bin/ppc*
Note:
I keep those 2 files in step #2 because I want to keep some setttings I configured for Lazarus. You can delete them if you want.