i want to reset my lumia 710 becous there are 2GB of reserved space and i want to put more music in the device. is i make the reset how can i have my purchased apps? i need to buy again?
You can go to windowsphone.com, click on Account & see a list of all apps you've purchased & click 'Reinstall' - it'll send the app OTA to your phone.
From your phone, it is a bit less intuitive. If you get to the app you want, you have to click the 'Buy' button, at which point it should tell you 'you've already purchased this app, would you like to download it?' - but it is dependent on having the same Live ID tied to your phone.
The way I (used to) do it (before Reinstaller was released) is fire up the Zune software PC-side and go to your purchase history (under settings>>account or something) it'll load apps by purchase date, including free ones. Type them into the marketplace on your phone and install.
As someone else said, Reinstaller works great - it's free on the marketplace as well.