I am not sure how to get upp strenght, defense, hp etc

I know i can buy it but its sold out

The equipments are not sold out...
you need enough zenies to buy the equipments
If you want to check what does it increase..click the scan item at the far right..

Well all the store upgrades are gone (but will come back) in the mean time you can still buy weapons to increase stats. After you have bought a weapon you can upgrade them in Synthesis (top right corner next to Adventure Mode). You can only upgrade a weapon three times.

ok... thanks i think i understand now