Hi all, how can I repartitionize an existing linux installation?

My disk is now like:
sda1;/boot;45.4 Mb (72.5% used)
sdb1; /usr; 20.4 Gb (26.9% used)
sdb3;/home;10.4 Gb (5.5% used)
sdb5;/;370.7 Mb (97.8 % used) !!!!
sdb6;/var; 249.7 Mb (83.9 % used) !!!!

A guy maded this configuration two years ago. Now I should repartitionize the Pc without formatting (many configurations)

Thank you for any suggestion