How can I root my Galaxy S5? It was At&t, i brought it over to Straight Talk

I purchased my friends S5 which was from AT&T and then I used the BYOP plan with Straight Talk. How do I root this? I tried Towelroot and it says its not supported. Also what ROMs can I get with this if any? I want to root to get rid of all the at&t pre installed apps on here that I cant use with Straight talk. Also pretty new to this. I have Odin on my laptop from installing stock firmware on my S3. Any help with root and ROMs would be much appreciated.

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