I made the install like this (
always worked!):
1./
Uninstall the previous version, even manually delete the .lazarus folder from home/user folder (of course, my projects are saved in other location).
2./
Download the 3 install files (fpc-laz,fpc-src,lazarus) from here:
https://www.lazarus-ide.org/3./
Copy these 3 files into 1 folder
4./ In the Terminal:
$ sudo apt-get install libgtk2.0-dev5./ In the Terminal open up the folder which contains the 3 files and
$ sudo dpkg -i *.debThat's it, you are ready!