There might not be anything wrong with your lens!
Yes, check what Carpents said.
Meanwhile, if the aperture blades are really stuck, you can try to go in by the back, but that way you can only clean the back of the blades, with everything in place.
To really clean everything (blade by blade), you must go in from the front of the lens. Mine (did it about a month ago) was a real pain to disassemble.
You can start by taking the front barrel out: just hold it and twist (not sure if to do this you don't have to release the focus ring first).
If I remember correctly, then you have to unscrew the second group of glass.
Then you have to take three "micro" screws out, to release the aperture assembly, but there is a large ring that's about 5 mm above those screws (hence you can't unscrew them), so first you have to take that off. This ring is screwed to the barrel at the end opposite to the aperture assembly.
In my case, that piece was screwed in so tight I just couldn't remove it
I had to put that thin lubricant/anti-stuck/anti-rust in the threads, little by little, and leave it to sink in about 3 or 4 days, before it came off!
After that, you can remove those 3 "micro" screws, and the whole aperture assembly just slides off the barrel.
One last pointer: be VERY careful with the little shaft that sticks out of the aperture assembly and makes it open/close. It's kinda fragile (yes, I broke mine off, and it was a PAIN to fix it - DON'T DO IT! ).
Hope this helps.
Nikon: D7000; F2; F4; FA. RMC Tokina 17/3,5; Ensinor 24/2,8 Macro; Nikkor: S.C. 50/1,4; AI-s 28/2,8; Micro 55/2,8; 80-200/4; S. E: 35/2,5; 100/2,8; Viv. S. 1 105/2,5 Macro (Kiron); MC Rokkor PG 58/1,2; Canon FD 300/4; Pentacon 135/2,8.
Pentax: K20D; CZJ Flek 20/4; SMC Pentax: A 28/2,8; 50/1,7; M 50/1,4; Tak. 50/1,4; Tamron Adall 2: SP 90/2,5 Macro; SP 60-300; 35-70/3,5 CF; .
And some others...