Resize smallfile tablespace - ORA-01144
You have two options.

Your current limit with smallfiles is 2G.  As you can see there the limit is 4194303 blocks, which is 4194303 x 512 byte block size = 2,147,483,136 bytes = 2G.


  Option 1:


Mount your file systems with the -largefiles option, which will allow you to create 32G and higher.


  Option 2:


You can only add 2G datafiles.

alter tablespace UNDOTBS1 add datafile 'path/filename' size 2G;


The -largefiles option has been the default for many years now, so there shouldn't be a problem for your unix admin to change this.