Alex,
English not a problem. Remove the cover over the engine and find the Fuel Pressure Regulator (FPR) which is inserted in the rear driver's end of the fuel injector connector rail. Start the car and remove the vacuum line which is attached to the nipple on the FPR. If there is any fuel present in the nipple then you must replace the FPR (if it has failed it will cause a very rich fuel mixture). The FPR is retained by a hairpin clip, and uses 2 O-rings for seals. Very simple replacement.
www.rockauto.com or Luke, in Parts at Lindsay Cadillac, M-F, 9-5 EDT (+4 GMT), over there >>>>>
Otherwise, I do not know about the procedure for change from gasoline to LPG.