Sometimes they are covered in a polymere and you can atack it with almost anything like mild detergents such as fairy etc, but I would be carfull just in case, If having a go always use safe cleaning practises like testing an area first that wouldent be visable "not easy in this case" and start from bottom and work your way up to prevent run marks aplying chemicals to a tery towle and not the screen
But I would consider using solvents for this as water might not do it any good :
Could be a job for a CC'er but might be cheeper in that case to buy a new one
Ive posted a link in the CC'er section to your post, as there might be a chemical out there suitable for the job that im not aware of like Ultrapac Renovate