Increase Max Upload Size from 2Mb

Hey guys im very new to wordpress. I’m trying to increase the maximum upload size from 2Mb to about 15Mb – I’ve tried using a free plugin to change it and it says the maximum upload speed is 19Mb after changing it – however my 8Mb picture is still not uploading (says something about phi.file).

I’ve read before that you have to go into theme files and add/change some code – however when i went to do this it said if i made some changes it could effect the whole website. As it’s just been created i’m a bit hesitate to do this. So not quite sure what to do now.

Thanks in advance for your help guys!.

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