You can find out how to update your firmware
here. Though you won't be able to use the first version instructions as you can't see your screen, I've not tried the other way, you'll need EOS utility installed & connect your camera to your PC.
When I've had camera problems, I've dealt direct with my local Canon Service Centre (luckily there is one just 25 miles from me). If the camera is still under warranty you just need produce the receipt & they will do do any work under the warranty, if it's not you'll need to pay. If you return it to the shop they will just send it to Canon who then send it back to the shop who send it to you, so it could take 2 weeks in transit without the time to examine it. On the 3 occasions I've popped my camera in, Canon has it sorted in 1-3 days & I collected it on the day it was ready.
I have found the Elstee Service Centre to be excellent; they do the work & always give the camera a clean & clean the sensor too.
However, once you go direct to Canon my understanding that returning it to the seller can be problematic should you need to in future under warranty.
Technically, you do have more protection under the Sale of Goods Act than you do with the warranty, which gives you 6 years' protection rather than just the year with a warranty, however, getting a retailer to accept any responsibility under the sale of Goods Act can be a battle & if they do accept liability they are entitled to knock off the value of wear & tear over the time you've had the item, if it needs to be repaired or replaced.
I have found Consumer Direct very helpful advising about your rights under the Sale of Goods Act, you can ring them for advice & will be given a reference number for any future calls should you have further problems with the retailer, their website is
here.
Good luck, I hope it gets sorted for you