i want to upgrade my IMac OS X Lion 10.7.5 to the last os, it say error. Someone help me to get it

hello,

i have imac with 10.7.5 version .

i tried to upgrade, downloaded the last os version el capitan using the apple support link for upgrade,

then when i use the get button i got a reply from the app store :

We could not complete your purchase.

INSTALL_ERROR_DISTRIBUTION_SIGNED_BY_APPLE

i want to upgrade my IMac OS X Lion 10.7.5 to the last os, it say error. Someone help me to get it

thank you

kochvan

.