Recharging the AC happens because of a leak.  If it was recharged two years
ago, then it is most probable, that it has leaked down again.  Unless you
have some expensive tools and lots of spare time, it is best to leave this
to the experts.  Try to find a locally owned business with a good reputation
for competence and honesty.  Good luck!

In the U.S. they sell recharge kits, consisting of a can of refrigerant, a
recharge hose, a pressure gauge and a fitting that couples to the vehicle's
AC system.  Sometimes this will get you through a season, but if you do not
find and fix the leak, then you will be back at the same spot next year.  It
is possible too, for an amateur to over-charge the system, which can be bad
for it.  (It is possible, but assumed less likely, for professionals to make
mistakes too.)

Earle