First take a backup of files you want
Then Boot up into the Livecd of Linux Mint, after it has loaded enter Gparted into the filter textbox of the Mint Menu. Then click on Gparted from the menu.After Gparted was loaded, you will see a list of all the partitions on your system.check for partitions Windows 7 created in your system
To delete windows 7 right click on its partitions and click delete. The windows 7 partitons will be the NTFS partitons if your not sure. You should now see 2 operations listed at the bottom of Gparted.Note that Gparted wont actually perform these operations until we tell it to. It may look like on Gparted that the Windows 7 partitions have now gone but their still there.
To resize the partition right click on it and click 'resize/move'. Drag the right arrow of the partition all the way to the right
Right click on the swap partition and click 'resize/move' now drag and move the coloured box with the two arrows all the way to the right.Then click the 'resize/move' button.Now we can resize the Linux Mint partition, right click it and click 'resize/move' then drag the right arrow to the right as far as you can then click the 'resize/move' button.
removing the Windows 7 entries from the grub menu.just login into Linux Mint, open the terminal and enter
> sudo update-grub