how to learn the cycloneIII in-depth

i have work in FPGA abount 2 years , but i find that i have only know the sample FPGA knowledge for cycloneIII . i only write the sample interfance for example ,IIC,245,SPI ,and use sram and ad . most of the time ,i am debugging timing 。

i think i will be change a job next year . then i want to know ,how to learn the fpga in-depth .

can you give me a idea ??

thank you very much