1) First of all, you need to check if this size isn't maximal in your server. You need to visit Stuido->Dashboard->Host tools area and launch there "Server audit" button. Find there the values of the 2 variables post_max_size and upload_max_filesize. These values are presented in Bytes so you need to divide them on 1024 and again on 1024 - then you will get the size in Megabytes. So if these values aren't fine for you then you need to ask your hosting support to increase them.
2) It can be done via Polyglot app In Studio area. Just go to the "Keys" area there and enter the "Search" field text, which you want to change (like "add/edit pictures"). Then edit the values of the found key.