It's quite easy to do , but a bit long winded. Download Easeus Partition Master, click on 'Free Edition' Easeus
Use it to view all partitions and space on the drive. You will need to MOVE each partition along to the end of the free space until the free space is contiguous with C: and then you can extend C: to contain this free space. Do it one partition at a time and don't forget to APPLY changes each time. Personally I would do it as quite a lot of programs will save or create temp files on C: and, depending on how many programs you have on your drive and how fastidious you are with housekeeping, you could easily find yourself running low on space on the C: drive. This may noticeably slow your computer and negate the gains of an SSD drive.