Firstly, I would recommend contacting your countries Lenovo Support Centre as it may not cost a lot to have it replaced by them.
Failing that and if you are up to it, the Hardware Maintenance manual should have all the instructions you need to replace the digitizer.
The instructions you'll need for removing and replacing the LCD assembly start on page 48 here. You will however need to go back as far as page 33 (1010 Keyboard) and work through to 1090 LCD unit.
NOTE: While Lenovo do freely release part replacement documents for their products, I would still recommend having the part replaced by a certified technician.