Could be that Lenovo does not have for Windows 10. I would suggest a dual boot and checking whether your laptop can actually manage to scavenge all necessary drivers for Windows 10.
I am not sure it works that way. By using dual boot, all you need to spare is some free space ( a drive to be exact ). Once you have dual boot, boot using Windows 10 see if you can get necessary drivers to get it working. If you can, stay with it and keep or delete Windows 7 as per you choice.
If you convert the disk to GPT, you will loose the present partitions. The only option is to take backup of data, convert disk to GPT and try installing Windows 10.
- - - Updated - - -
Refer this: *technet.microsoft.com/en-us/library/cc725671.aspx