How to update PostGIS 2.1 to use `ST_DelaunayTriangles()`

The error "lwgeom_delaunay_triangulation: GEOS 3.4 or higher required" arrives on my terminal, running psql with

SELECT PostGIS_Lib_Version();
--   2.1.4

SELECT postgis_version();
-- 2.1 USE_GEOS=1 USE_PROJ=1 USE_STATS=1

and when use use ST_DelaunayTriangles() (ex. in this script).

So, what is the problem, how re-install PostGis or workaround it?

---

EDIT for @janechii suggestion,

 select PostGIS_full_version();

POSTGIS="2.1.4 r12966" GEOS="3.3.3-CAPI-1.7.4" 
PROJ="Rel. 4.7.1, 23 September 2009" GDAL="GDAL 1.9.0, released 2011/12/29" 
LIBXML="2.8.0" LIBJSON="UNKNOWN" TOPOLOGY RASTER

PostGIS was installed all by standard apt-get in my Debian Stable this week, and now redo (try reinstall GEOS to use 3.4 not 3.3) with

sudo apt-get -y install postgis postgresql-9.3  libgeos-3.4 libgeos-c1 libgeos-dev

but no effect.

Answer

After all @janechii clues.... and purging all possible residuals,

 sudo apt-get purge build-essential libgeos-3.4 libgeos-c1 libgeos-dev  libxml2-dev libgdal-dev libproj-dev libjson0-dev xsltproc docbook-xsl docbook-mathml
 sudo apt-get purge postgis

I statart with (adapting!) recipes of this link:

 wget http://download.osgeo.org/geos/geos-3.4.2.tar.bz2

 tar xfj geos-3.4.2.tar.bz2
 cd geos-3.4.2
 ./configure
 make
 sudo make install
 cd ..

At here ok geos 3.4 there (!). Then...

 wget http://download.osgeo.org/postgis/source/postgis-2.1.3.tar.gz
 tar xfz postgis-2.1.3.tar.gz

 cd postgis-2.1.3
 ./configure
 sudo make install  

this last make trigg a "configure: error: the PGXS Makefile (...) cannot be found. Please install the PostgreSQL server development packages and re-run configure". So, as some more clues here do

 sudo apt-get install postgresql-server-dev-9.3

so red config,

 ./configure

then ok, a good msg:

  PostGIS is now configured for x86_64-unknown-linux-gnu

  -------------- Compiler Info ------------- 
    C compiler:           gcc -g -O2
    C++ compiler:         g++ -g -O2
    SQL preprocessor:     /usr/bin/cpp -w -traditional-cpp -P

   -------------- Dependencies -------------- 
    GEOS config:          /usr/local/bin/geos-config

    GEOS version:         3.4.2
  ...
   --------------- Extensions --------------- 
    PostGIS Raster:       enabled
    PostGIS Topology:     enabled
    SFCGAL support:       disabled

   -------- Documentation Generation -------- 
    xsltproc:             /usr/bin/xsltproc
    ....

Then, continue:

 make
      # PostGIS was built successfully. Ready to install.
 sudo make install
 sudo ldconfig
 sudo make comments-install


 sudo ln -sf /usr/share/postgresql-common/pg_wrapper /usr/local/bin/shp2pgsql

 sudo ln -sf /usr/share/postgresql-common/pg_wrapper /usr/local/bin/pgsql2shp
 sudo ln -sf /usr/share/postgresql-common/pg_wrapper /usr/local/bin/raster2pgsql


 psql -h localhost -U postgres postgres
 CREATE EXTENSION postgis;
 CREATE EXTENSION postgis_topology;
 \q

Then, testing with this script... OK!!!!